Vaccination Status Research Articles

P-685. Investigation of Influenza antibody transfer following maternal vaccination using the PREVAIL Birth Cohort

Abstract Background Seasonal influenza vaccine is recommended during pregnancy; however, data are limited on transplacental antibody transfer. We used the PREVAIL Cohort of healthy, term infants and their mothers in Cincinnati, Ohio, to describe hemagglutination-inhibition (HAI) titers in pregnancy and measure the association between maternal and cord HAI relative to maternal vaccination during pregnancy.Table 1.Maternal GMT by Vaccination Status and by Influenza A Subtypes and Influenza B Lineages Methods Maternal immunization status was abstracted from medical charts/state registries. HAI titers were measured in maternal blood collected in the third trimester, and in cord blood. HAI > 1:40 were considered seroprotective. Paired T tests (log normal distribution) and Fisher’s exact tests were used to compare geometric mean titers (GMT) and proportion of participants with seroprotective HAI, respectively, for each influenza subtype/lineage by vaccination status. Association between maternal and cord HAI was assessed using Spearman correlation and Maternal HAI/Cord HAI ratios.Table 2.Maternal Seroprotection by Vaccination Status and by Influenza A Subtypes and Influenza B Lineages Results 155 mothers were included and delivered in the 2017-2018 influenza season (July 1st 2017-June 30st 2018); H3N2, H1N1 and B viruses circulated this season. 105 mothers received influenza vaccine during or 4 months prior to pregnancy. Vaccinated mothers had significantly higher GMTs for all influenza subtype/lineage compared to unvaccinated mothers (p< 0.005) (Table 1). A significantly higher proportion of vaccinated mothers exhibited seroprotective titers against influenza subtype/lineage H3N2 and B-Victoria compared to unvaccinated mothers (p< 0.05) (Table 2). There was a significant correlation between maternal and cord blood HAI for all subtype/lineage (r > 0.85, p< 0.05) (Figure 1). Cord GMTs tended to exceed maternal GMTs, with statistically significant differences in Influenza B lineage (p< 0.05) (Table 3). More than 75% of the mother-infant pairs exhibited transplacental antibody transfer ratios ≤ 1.Table 3.Maternal GMT and Cord GMT by Influenza A Subtypes and Influenza B Lineages Conclusion Vaccinated mothers displayed protective influenza antibodies levels which were significantly higher than those found in unvaccinated mothers. Maternal HAI was strongly correlated with cord HAI, suggesting efficient transplacental transfer. Moving forward, investigation of factors influencing this transfer will be undertaken.Figure 1.Scatter plots of maternal vs cord log-transformed HAI titers Disclosures Mary A. Staat, MD, MPH, Cepheid: Grant/Research Support|Merck: Grant/Research Support|Pfizer: Grant/Research Support|Up-To-Date: Honoraria

427. Underlying Medical Conditions and Vaccination Status among U.S. Children Aged ≤17 Years Hospitalized for COVID-19 in COVID-19-Associated Hospitalization Surveillance Network (COVID-NET), January–December 2023

Abstract Background SARS-CoV-2 infection can result in serious illness in children. We used COVID-19-Associated Hospitalization Surveillance Network (COVID-NET) data to assess characteristics associated with pediatric COVID-19 hospitalizations, including underlying medical conditions and vaccination status. Percent of COVID-19-Associated Hospitalizations† with Specific Underlying Medical Conditions among U.S. Children Aged ≤17 Years by Age Group — COVID-NET, January–December 2023 Methods U.S. children aged ≤ 17 years with COVID-19 as the likely primary reason for hospitalization during January–December 2023 were identified in the population-based COVID-NET active surveillance system, which includes patients residing in a catchment area of > 300 acute care hospitals in 13 states with a positive SARS-CoV-2 test result during or ≤ 14 days before admission. Medical records of a random sample of children stratified by age-group and site were abstracted; reported percentages were weighted to account for probability of selection. We assessed patient age, underlying medical conditions, and receipt of vaccine dose within 12 months before illness. Results Of 2016 children hospitalized for COVID-19, 1232 (61%) were aged < 2 years (611 aged < 6 months; 621 aged 6–23 months). Overall, 51% had no underlying condition, including 73% of infants aged < 6 months, 58% of children aged 6–23 months, and 24% of children aged 12–17 years (Figure). Among children aged < 2 years, prematurity was the most common underlying condition (17–20%). Neurologic disorders (27–31%) and asthma (21–33%) were most prevalent among children aged ≥ 2 years. Among 1379 children aged ≥ 6 months eligible for vaccination with vaccine data available, only 14% had received ≥ 1 vaccine dose within 12 months before illness, with the lowest frequency (9%) among children aged 6–23 months (Table). Among age-eligible children with neurologic disorders and asthma, only 18% and 16% were vaccinated, respectively. Conclusion Most children aged < 2 years hospitalized for COVID-19 during 2023 had no underlying conditions; underlying conditions were more prevalent among older children. More than 85% of age-eligible children had not received a vaccine dose within 12 months, including among children with underlying conditions. Increasing pediatric COVID-19 vaccination, especially among children with underlying medical conditions, could help reduce COVID-19 hospitalizations. Disclosures Anna Falkowski, Master of Science, Council of State and Territorial Epidemiologists (CSTE): Grant/Research Support

P-1436. Patient dissatisfaction increases the odds of inconsistent influenza vaccination completion following the onset of the COVID-19 pandemic

Abstract Background The COVID-19 pandemic has underscored challenges with patient adherence to medical directives, particularly vaccine acceptance. While sociodemographic factors have been linked to non-COVID-19 vaccine hesitancy, the relationships between patient experience, the COVID-19 pandemic, and adherence to routine vaccinations are uncertain.Figure 1:Yearly influenza vaccine refusal, influenza vaccine administrations, and overall patient satisfaction since establishing care with a primary care provider from 2017-2023.Panel A (Influenza Refusals): the number of vaccine refusals among individuals who are Intermittently Vaccinated and Never Vaccinated for seasonal influenza since establishing care with a primary care provider over time.Panel B (Influenza Vaccinations): the number of vaccines administered over time since establishing care with a primary care provider among those who are Always Vaccinated and Intermittently Vaccinated for seasonal influenza.Panel C (Overall Satisfaction): the number of patients who indicated that they were maximally satisfied with their overall care following any interaction with the healthcare system over time. Methods We retrospectively analyzed influenza vaccination records of adult primary care patients in Olmsted County, Minnesota. Vaccination history was examined during two phases: Pre-Pandemic (1/1/2017—2/28/2020) and Pandemic-Plus (3/1/2020—12/31/2023). Vaccination status was defined as “always vaccinated” (AV), “never vaccinated” (NV), or “intermittently missed years of vaccinations” (IV) for seasonal influenza. Patient dissatisfaction was determined if patients negatively ranked their overall quality of care on standard patient experience surveys. We explored the relationship between influenza vaccination rates, healthcare engagement, and patient satisfaction.Figure 2:Multinomial logistic regression of patient satisfaction on vaccination status across the phases of the COVID-19 Pandemic, adjusted for engagement in the health care system, participation, and area of deprivation index (ADI) for patients that were (A) intermittently vaccinated compared to always vaccinated and (B) never vaccinated comparted to always vaccinated. The “Pre-pandemic phase” refers to influenza immunization data and patient satisfaction data prior to March 2020. The “Pandemic-plus phase” refers to immunization data and patient satisfaction data from March 2020 to January 2024. Low ADI ranking refers to areas with a low level of deprivation, whereas high ADI ranking refers to areas with a high level of deprivation. Individuals were considered low if they came from an area with a state ADI ranking from 1 to 5 and were considered high if they came from an area with a state ADI ranking from 6 to 10. Results From 1/1/2017 to 12/31/2023, 21% of individuals were AV (n=36,632), 52% were IV (n=90,776), and 27% were NV (n=46,418) for seasonal influenza. Post-pandemic onset, 7% (n=3,556) of the Pre-Pandemic AV and 32% (n=16,710) of the Pre-Pandemic IV never received another influenza vaccine. In the Pandemic-Plus phase, the IV and NV had a higher likelihood of disengagement with the healthcare system [odds ratio (OR) (95% CI): 1.59 (1.55, 1.64); 4.21 (4.09, 4.33)], residing in areas of greater deprivation [1.58 (1.53, 1.62); 1.99 (1.94, 2.05)], and self-identifying their race as Black [2.29 (2.09, 2.51); 3.29 (3.01, 3.60)] compared to the AV. After adjusting for healthcare engagement and area of deprivation, dissatisfaction OR increased from 1.03 (0.99,1.07) Pre-Pandemic to 1.07 (1.03,1.12) in the Pandemic-Plus phase among IV compared to AV. Similarly, the OR of dissatisfaction rose from 1.11 (1.05, 1.18) Pre-Pandemic to 1.16 (1.09, 1.24) in the Pandemic-Plus phase among those who were NV compared to those AV. Conclusion Higher healthcare dissatisfaction was observed among those inconsistently adherent to vaccination recommendations. Targeted efforts to enhance patient satisfaction may boost vaccination rates. Disclosures All Authors: No reported disclosures

P-1912. Characteristics and Outcomes of Matched Vaccinated and Unvaccinated Patients Hospitalized for Covid-19 in 27 Hospitals During Brazil's Delta and Omicon Waves

Abstract Background Brazil faced significant challenges during the COVID-19 pandemic, emerging as one of the most affected countries globally in the number of cases and deaths. In January 2021, the country began the national vaccination campaign against COVID-19. Currently, about 80.2% of Brazilians over six months of age are fully vaccinated. Few population-based studies have compared clinical characteristics and outcomes among patients hospitalized for COVID-19 concerning vaccination status. This knowledge gap was even greater when an attempt was made to match vaccinated versus unvaccinated individuals to control for confounders. Therefore, this study aimed to compare the clinical characteristics and outcomes of matched vaccinated and unvaccinated COVID-19 in hospital patients. Flowchart of COVID-19 patients included in the study. Methods This retrospective multicenter cohort study included adult COVID-19 patients, with a laboratory-confirmed diagnosis, from 27 hospitals, admitted from March/2021 to August/2022. Clinical characteristics, vaccination status, and outcomes were collected from medical records. Vaccinated and unvaccinated patients were compared in a matched analysis, using the propensity score model that included age, sex, hospital, and comorbidities (hypertension, diabetes mellitus, obesity [body mass index > 30kg/m2], heart failure, and chronic kidney disease). Results From 3,188 patients, 1,963 (61.6%) were unvaccinated and 1,225 (38.4%) fully vaccinated. Among these, we matched 771 vaccinated with 771 unvaccinated. Vaccinated had lower rates of mortality (17.6% vs. 29.7%), invasive mechanical ventilation (IMV-17.5% vs. 33.0%), non-invasive mechanical ventilation (NIMV- 10.0% vs. 20.2%), intensive care unit admission (ICU- 29.8% vs. 44.0%) vasoactive drugs use (20.5% vs. 30.9%), dialysis (8.0% vs. 13.7%), p < 0.001 for all, and thrombosis (3.7% vs. 7.5% p=0.002). Conclusion This study suggests considerable benefits of vaccination for patients hospitalized with COVID-19. Fully vaccinated patients experienced lower mortality rates and lower severity disease with fewer ICU admissions, and shorter hospital lengths of stay. These findings confirm that prior vaccination reduces the risk of death and alters the disease trajectory in hospital settings. Disclosures All Authors: No reported disclosures

P-1951. Incidence of SARS-CoV-2 Infection among those 6 Months to 49 Years of Age in the Cascadia Prospective Cohort Study, Oregon and Washington, United States, July 1, 2022 – March 31, 2024

Abstract Background With the ending of the public health emergency and changes in the testing landscape, less is known about SARS-CoV-2 incidence in the community than earlier in the pandemic. Our goal was to describe SARS-CoV-2 incidence among individuals 6 months to 49 years of age enrolled in the Cascadia prospective community cohort study in Oregon and Washington, USA, by age, sex, and COVID-19 vaccination status. Covid-like illness (CLI) and vaccination status definitions Methods We included Cascadia participants enrolled July 1, 2022 – March 31, 2024. We collected weekly nasal swabs and surveys from participants; more frequently among those with SARS-CoV-2 infection. We defined SARS-CoV-2 infection as a positive or inconclusive swab result and assessed covid-like illness (CLI) symptoms ±7 days from collection date (Fig.1). We followed individuals from receipt of their first nasal swab until the earliest of SARS-CoV-2 infection, loss to follow-up, or the end of the study period. We considered age and COVID-19 vaccination status (Fig. 1) as time-varying variables. We estimated incidence as the number of SARS-CoV-2 infections per 1,000 person-weeks (p-w) of observation, along with robust-error 95% confidence intervals (CI); we considered incidence rates to vary between strata if confidence intervals did not overlap. Table Incidence of SARS-CoV-2 Infection among Cascadia study participants, by sex, age, and vaccination status, July 1, 2022-March 31, 2024 Results We observed 1,495 SARS-CoV-2 infections among 3,464 included individuals with 164,290 p-w of follow-up; overall incidence rate was 9.10 (CI 9.09, 9.11). Incidence was similar by sex, lowest among those 6m-4y, and highest among those 12-17y (Table). Overall SARS-CoV-2 incidence was higher among those previously up-to-date (10.17 [CI 9.24, 11.18]) than among those currently up-to-date with vaccines (8.42 [CI 7.72, 9.19]; Table). A quarter (178/716) of SARS-CoV-2 infections among those < 18y were asymptomatic, compared with 10% (76/785) among those ≥18. The proportions reporting ≥2 CLI symptoms were 54% (49/91) among those 6m–4y, 62% (219/354) among those 5–11y, 69% (184/265) among those 12–17y, and 85% (666/785) among those 18–49y (Fig. 2). Frequency of covid-like illness (CLI) symptoms1 reported among Cascadia study participants, by age, July 1, 2022-March 31, 2024 Conclusion Our study fills a knowledge gap about the incidence of SARS-CoV-2 in the community later in the pandemic. Incidence was lowest among those recently vaccinated. These findings will inform continued discussions about COVID-19 vaccination strategies. Disclosures Mark A. Schmidt, PhD, MPH, HilleVax: Grant/Research Support|Janssen: Grant/Research Support|Moderna: Grant/Research Support|Pfizer: Grant/Research Support|Vir Biotechnology: Grant/Research Support Neil D. Yetz, M.P.H., N/A: Expert Testimony Teresa Kimes, MS, Moderna: Grant/Research Support|Vir Biotechnology: Grant/Research Support Stephen P. Fortmann, MD, Pfizer: Grant/Research Support Holly C. Groom, MPH, Hillevax: Grant/Research Support|Moderna: Grant/Research Support Jennifer L. Kuntz, MS, PhD, Hillevax, Inc: Grant/Research Support Richard A. Mularski, MD, MSHS, MCR, Pfizer, Inc: Grant/Research Support Janet A. Englund, MD, Abbvie: Advisor/Consultant|AstraZeneca: Advisor/Consultant|AstraZeneca: Grant/Research Support|GlaxoSmithKline: Advisor/Consultant|GlaxoSmithKline: Grant/Research Support|Meissa Vaccines: Advisor/Consultant|Merck: Advisor/Consultant|Pfizer: Board Member|Pfizer: Grant/Research Support|Pfizer: Speaker at meeting|SanofiPasteur: Advisor/Consultant|Shinogi: Advisor/Consultant Helen Y. Chu, MD, MPH, Abbvie: Advisor/Consultant|Merck: Advisor/Consultant|Vir: Advisor/Consultant

P-1461. Influenza Vaccine Amongst Persons Experiencing Homelessness: Evaluating Attitudes, Barriers, and Trust

Abstract Background In Detroit, persons experiencing homelessness (PEH) have been a vulnerable part of society due to their comorbidities and unique barriers in access to care. Despite PEH experiencing higher rates of vaccine-preventable diseases, there is a lack of information on strategies to improve vaccine rates. The objective of this project is to obtain an understanding of enablers and barriers in influenza vaccine uptake amongst PEH, to inform future work to increase vaccine uptake. Methods This is a cross-sectional study of survey data from adult PEH encountered during Street Medicine (SM) outreach in Detroit to assess enablers and barriers in influenza vaccination. Respondents were provided a complimentary bus pass for participation. Descriptive statistics were conducted on sociodemographic variables with analysis of variables related to level of homelessness, vaccine concerns, vaccination status, and underlying health problems. Results 43 participants' surveys were analyzed. Participant vaccine status and level of homelessness varied with majority (35%) reporting spending at least 1 night in a tent or other dwelling. Regarding participant demographics, 86% (n=37) were male and 81% (n=35) were Black or African American (AA) (Table 1). Amongst survey respondents, the highest sources of trust for information regarding influenza vaccine was found amongst: ‘Social Services Agencies or Other Services’ 95.2% (n=20) and ‘Experts and Scientists’ 93.8% (n=15) (Figures 1 and 2). Variables regarding sources of information trusted were analyzed via chi-square analysis to evaluate for statistical significance (p-value < 0.05) amongst demographic variables (Figure 3). Conclusion Previous literature regarding attitudes towards vaccines amongst PEH has demonstrated distrust in healthcare. Results of this study are unique in identifying healthcare members as resources trusted by most participants in providing information on vaccines. This emphasizes the importance of SM outreach in Detroit in building trusting relationships with PEH in addition to decreasing barriers in access to care, to help target future vaccination initiatives.Table 1:Participant Demographics and Influenza Vaccination Status Disclosures Seema Joshi, MD, AbbVie: Grant/Research Support Marcus Zervos, MD, Johnson and johnson: Grant/Research Support|Moderna: Grant/Research Support

P-1977. Six-Month Trajectory of Symptoms of COVID-19 Fatigue by Age and BNT162b2 COVID-19 Vaccination Status: A Prospective Study among Symptomatic US Adults Testing Positive for SARS-CoV-2 at a National Retail Pharmacy

Abstract Background Fatigue is one of the most common symptoms experienced by patients with COVID-19, potentially interfering with daily activities. This study assessed the 6-month trajectory of fatigue from time of testing across age and BNT162b2 BA.4/5 bivalent COVID-19 Vaccine strata.Figure 1.Prevalence of symptoms of fatigue across groups defined by age and BNT162b2 COVID-19 Vaccination statusa) Overall cohort by BNT162b2 vaccination status Methods Symptomatic US adults testing positive for SARS-CoV-2 at CVS Health were recruited between 03/02-05/18/2023 (CT.gov: NCT05160636). Study participants self-reported symptoms of fatigue via an online survey during the acute (testing day, Week 1, Week 2) and long-term phase (Week 4, Month 3 and 6 after testing). The prevalence of fatigue was evaluated at each time point in the overall cohort and across groups defined by vaccination status and age (older adults: ≥50; younger adults: < 50). Between-group differences were tested by using chi-square statistics. b) Overall cohort by age Results The analyses included 643 study participants: 49% (316) vaccinated with BNT162b2 bivalent and 51% (327) unvaccinated; 43.1% (277) ≥50 and 56.9% (366) < 50 years old. A total of 424 (65.9%) participants self-reported symptoms of fatigue at time of testing. Their mean age was 46.5 years, 71.2% were female, 25.9% had ≥1 comorbidity, 43.2% had prior infection. The presence of fatigue was higher during the acute phase and remained prevalent during the long-term follow-up: 50.9% at Week 1, 41.1% at Week 2, 24.4% at Week 4, 19.6% at Month 3, and 18.5% at Month 6 (Figure 1a). While older and younger adults had similar prevalence of fatigue during the acute phase, at Week 4 the younger adults reported higher prevalence (28.7% vs 18.2%, p=0.007) (Figure 1b). In the overall cohort, and relatively consistently across age groups, those vaccinated with BNT162b2 reported significantly (p< 0.005) lower prevalence of fatigue at Week 4, Month 3 and 6 (Figures 1a, 1c, 1d). c) Younger adults (<50) Conclusion This study found that fatigue is a highly prevalent symptom affecting two-thirds of symptomatic adults at time of testing. While prevalence declined over time, fatigue symptoms persisted beyond the acute phase, with 1 in 5 still affected at Month 6. Compared with those vaccinated with BNT162b2 bivalent, the prevalence of fatigue was higher among unvaccinated throughout the follow-up, reaffirming the value of being up-to-date with COVID-19 vaccination. d) Older adults (≥50) Disclosures Manuela Di Fusco, PhD, Pfizer Inc.: Employee|Pfizer Inc.: Stocks/Bonds (Public Company) Alexandra Berk, PhD, CVS Health: Employee|CVS Health: Stocks/Bonds (Public Company) Kristen E. Allen, MPH, Pfizer Inc.: Employee|Pfizer Inc.: Stocks/Bonds (Public Company) Thomas M. Porter, MPH, Pfizer Inc.: Employee|Pfizer Inc.: Stocks/Bonds (Public Company) Mary B. Alvarez, PharmD, Pfizer Inc.: Employee|Pfizer Inc.: Stocks/Bonds (Public Company) Joseph C. Cappelleri, PhD, Pfizer Inc.: Employee|Pfizer Inc.: Stocks/Bonds (Public Company) Mary M. Moran, MD, Pfizer Inc.: Employee|Pfizer Inc.: Stocks/Bonds (Public Company) Xiaowu Sun, PhD, CVS Health: Employee|CVS Health: Stocks/Bonds (Public Company)

P-1455. Socioeconomic and Regional Impact on Influenza Vaccination in Young Children During the COVID-19 Pandemic

Abstract Background Influenza (flu) vaccination reduces hospitalizations and severe illness, especially in young children particularly vulnerable to complicationsTable 1:Comparison of Influenza Vaccination Rates and Associated Predictors Among American Children Aged 0-5 Years in 2019 and 2022 This table provides an overview of key variables influencing flu vaccination rates among young children, showing changes between 2019 and 2022. It includes data on the total number of children surveyed, vaccination status, average age, gender distribution, educational levels of parents, family income quartiles, ethnic groups with the highest and lowest vaccination rates, insurance coverage, and whether the child had a doctor's visit in the past year. Methods Data from the National Health Interview Survey for 2019 and 2022 were analyzed to assess the impact of parental education, household income, health insurance, and race/ethnicity on flu vaccination rates among U.S. children ≤5 years. Employing logistic regression, Chi-square tests, and Mann-Whitney U tests in STATA, the potential influence of socioeconomic factors on influenza vaccination during the COVID-19 pandemic was evaluated.Table 2:Factors Influencing Influenza Vaccination Rates Among Young Children in the United States, 2019-2022: Results from Logistic Regression Analysis This table summarizes the logistic regression analysis results, presenting odds ratios, 95% confidence intervals, and p-values for predictors influencing influenza vaccination rates among young children aged 0-5 years. The analysis underscores the significant impact of the survey year, child's age, ethnicity, region, parental education, family income, insurance status, and recent healthcare interactions on vaccination likelihood. Results Records for 7636 children in 50 states were reviewed (2858 in 2019 and 4778 in 2022). Flu vaccination rates decreased from 56.02% in 2019 to 46.38% in 2022 (p < 0.001). The decline in flu vaccination rates was most pronounced among younger children, with rates for 2-year-olds reducing from 66.60% to 53.38%, 1-year-olds from 62.95% to 49.03%. and infants from 30.87% to 24.22% (p < 0.001). Insured children were more likely to be vaccinated than uninsured (OR=1.64, p< 0.001). A recent doctor's visit increased the likelihood of receiving a flu vaccine (OR=5.68, p< 0.001). Children from households earning ≥400% of the federal poverty level and those with college or above-educated parents had higher odds of vaccination (OR=1.93, p< 0.001 and OR=1.84, p=0.001, respectively). Significant regional variations in flu vaccination were noted, especially in the Southern U.S. (OR=0.70, p< 0.001). Racial differences were significant, with lower flu vaccination rates among non-Hispanic Black children compared to non-Hispanic Whites (OR=0.70, p< 0.001), while non-Hispanic Asian children exhibited higher flu vaccination rates (OR=1.32, p=0.018). Conclusion The decline in flu vaccination rates among young children during the COVID-19 pandemic highlights the influence of socioeconomic factors, healthcare access, and racial disparities on public health outcomes. Addressing these issues is crucial for improving vaccination rates and reducing influenza's impact on young children. Disclosures All Authors: No reported disclosures

P-1916. The impact of SARS-CoV-2 VOCs on clinical outcomes: an Umbrella Review

Abstract Background Studies aiming to synthetize data from literature are helpful to valid the robustness of associations, to assess the quality of the data, and, eventually, to propose recommendations. This is particularly evident for the huge amount of data reported for SARS-CoV-2. The aim of this study was to perform an umbrella review to identify the strength and validity of associations between variants of concern (VOCs) and pre-specified clinical outcomes in COVID-19 patients. Table 1 Effect size measures reported in the studies included in the review, divided by outcome. Acronyms: CI, confidence interval; OR: odds ratio; RR, risk ratio; cCFR, confirmed case-fatality risk; HFR, hospitalization-fatality risk; N/A, not available Methods An umbrella review according to the principles to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) was performed searching multiple databases in January 2024. Peer reviewed systematic reviews considering ≥ 2 VOCs with a clinical outcome among death, hospitalization, severe disease, admission to intensive care unit (ICU), and mechanical ventilation were included. Data on study population and measures of association between clinical outcome and VOCs were considered. The quality of the studies was assessed through the AMSTAR-2 tool. The effect size measures with the confidence interval for each association between VOCs and clinical outcomes were reported. Subgroup analyses were performed, if possible. A citation matrix was used to assess the overlap between the systematic reviews included. Table 2 Risk of bias assessment of the included systematic reviews using the AMSTAR-2 score. In bold the key domains. Results A total of 11 studies were included in our review. 24 total comparison were considered, most regarding Omicron versus Delta (19/24), where Omicron was always associated with better clinical outcomes than Delta. The overall quality of the studies was low. None of the reviewed studies incorporated consideration of risk factors other than VOCs in evaluating clinical outcomes. The overlap between the included reviews is low, only 10% of them having a significant overlap ( > 15%). Conclusion Our umbrella review shows the lower hazard on human health of the Omicron compared to Delta variant. However, the quality of the reviews included were generally low and there is a lack of correction with other risk factors such as comorbidities and vaccination status. While our review provides valuable insights into the association between VOCs and clinical outcomes of SARS-CoV-2 infection, further research incorporating risk factor analysis and ensuring methodological rigor is warranted. Disclosures All Authors: No reported disclosures

P-2066. Impact of XXB 1.5 Monovalent Booster Vaccination on Mucosal and Systemic Immune Responses in Healthy Adults

Abstract Background The FDA recently approved the first monovalent XBB1.5 booster vaccine. However, the mechanism by which this vaccine stimulates mucosal and systemic immune responses has been understudied.Figure 1.Impact of XBB 1.5 vaccination on viral neutralization titers using pseudo virus assay (left panel) and ACE2 inhibition assay (right panel).Each dot (white) represents a single serum sample tested in parallel with a post-vaccination sample (colored dot) for each of the 28 participants. The mean fold increase in neutralization titers pre- and post-vaccination are shown for Wuhan, XBB 1.5, and BA5 variants. All increases in neutralization titers are significant to P<0.0001 by employing Wilcoxon matched-pairs signed rank test. Methods We examined 28 participants' serum and saliva one week before and two to three weeks after the XBB1.5 mRNA vaccination for neutralizing and binding antibodies to Wuhan and XBB1.5 S protein.Figure 2:Inhibition of ACE2 binding to different S variants by saliva samples pre- and post-vaccination with XBB1.5 monovalent booster.Paired samples represent the percent ACE2 binding inhibition in participants before and after vaccination. Vaccination induced a 1.7-fold increase in ACE2 neutralization in saliva to XBB1.5 (p<0.0001) and 1.2-fold increase in ACE2 neutralization to Wuhan (p=0.03). Significance tested between pre and post-vaccination by Wilcoxon matched-paired sign rank test. *** p<0.001, **** p<0.0001. Results We observed a 2.9 to 2.6-fold and 5.0 to 7.8-fold increase in Wuhan and XBB1.5 serum neutralization titers following mRNA vaccination using pseudovirus and ACE2 neutralization assays respectively, that closely correlated with a rise in binding antibodies to S protein. Vaccination induced a 1.7-fold increase in ACE2 neutralization in saliva to XBB1.5 (p< 0.0001) and 1.2-fold increase in ACE2 neutralization to Wuhan (p=0.03). This increase in neutralization Ab levels in saliva failed to correlate with the number and time of prior COVID-19 infections, vaccination status, type of vaccine, or concomitant rise in S-specific IgA or IgG in saliva or serum. Depletion of IgA or IgG in saliva following vaccination demonstrated that IgA was primarily responsible for the increase in ACE2 blocking activity (mean reduction in blocking activity with IgA depletion=68%, range, 58-81%) compared to IgG (mean reduction=27%, range 0-71%).Figure 3.Role of IgA on percent reduction in ACE2 inhibition in saliva. Depletion of IgA or IgG in saliva following vaccination demonstrated that IgA was primarily responsible for the increase in ACE2 blocking activity (mean reduction in blocking activity with IgA depletion=68%, range, 58-81%) compared to IgG (mean reduction=27%, range 0-71%). Statistical analysis done using unpaired t test. Conclusion The XBB1.5 monovalent vaccine boosts systemic and mucosal viral neutralization antibody levels, primarily to the XBB1.5 variant. Most people have hybrid immunity to SARS-CoV2 now, so mRNA vaccines boost mucosal immune response better than observed earlier in the pandemic. Increased oral mucosal immunity may reduce the risk of COVID-19 progressing to pneumonia and more severe disease. Disclosures All Authors: No reported disclosures

P-2064. COVID-19 Vaccination-infection Status and Immunological Profile: Identification of High-Risk Population for Targeted Booster Immunization In India

Abstract Background The immunological profiles and predictors of immune response in people with hybrid immunity, resulting from a combination of natural infection and vaccination, particularly in regions where non-mRNA vaccines were administered, remain less understood. Methods This was a cross-sectional study done at AIG Hospitals, Hyderabad, India. Consecutive participants were enrolled, and sampled for immunological testing. The study population was divided into six cohorts based on their infection and vaccination status. Immunological assays were performed to measure anti-spike protein and interferon-γ release assay. Hospitalization rates were compared in all groups. Chi-square test was used to compare categorical variables, and the Mann-Whitney U test was used for comparing medians. Post-hoc Dunn test was used for pairwise comparison. Bonferroni adjustment for p-value was performed for multiple pairwise comparisons. Linear regression model was used appropriately to find predictors of antibody titres. Results A total of 1040 patients were enrolled in the study. The population was divided into six cohorts: Unvaccinated, Primary, Booster, Hybrid (Pre-Omicron only), Hybrid (Omicron only), and Hybrid (Both). Antibody titres and IGRA levels were found to be statistically higher in the Hybrid (both infection) group (Table 1 and Figures 1a & 1b). The linear regression model showed factors predicting antibody response (Table 2). Age and hypertension were independent (negative) predictors of antibody levels. During the follow-up (median 30.7 [26.6 – 34.4 months]) of 1008 patients, 770 (76.4%) had a documented COVID infection with Omicron. Hospitalization was evaluated in three groups: Hybrid, vaccination only and unvaccinated. The incidence was significantly lower in the Hybrid group; log-rank test: p < 0.001. (Figure 2) Conclusion The prevalence of hybrid immunity was high in the study population. Individuals above 60 years old and with comorbidities are more likely to have lower antibody titers. Immunized patients were protected against hospitalization. There is a need for prioritized immune-boosting efforts in high-risk individuals. Disclosures All Authors: No reported disclosures

P-603. Potential Public Health Impact of Respiratory Syncytial Virus (RSV) Vaccines for Prevention of RSV Among Older Adults in the United States

Abstract Background Two United States (US) Food and Drug Administration-approved vaccines are recommended by the Advisory Committee for Immunization Practices for prevention of lower respiratory tract disease (LRTD) due to respiratory syncytial virus (RSV) among US adults aged ≥ 60 years and another vaccine for adults is under regulatory review. We evaluated the potential public health impact of vaccines for prevention of RSV-LRTI in older adults. Methods A cohort model was employed to depict clinical outcomes and economic costs of RSV-LRTD over two years with use of alternative vaccines (ie, Pfizer’s RSVpreF, GSK’s RSVpreF3, Moderna’s mRNA-1345 respectively, vs no intervention) among a cohort of 2.4M adults aged ≥ 60 years in a hypothetical US health plan with 10M beneficiaries. Clinical outcomes were projected (monthly) based on age, comorbidity profile (ie, with vs without chronic or immunocompromising medical conditions), RSV-LRTI disease rates (requiring hospitalization [H], emergency department [ED], or physician office/hospital outpatient care [PO/HO]), calendar month, case fatality rates (RSV-H only), and vaccination status (23.6% uptake in October of model year 1 only). Initial vaccine effectiveness (VE) and waning of VE was derived from published or presented Phase III clinical trial data. Economic costs were generated based on cases and corresponding unit costs. Results Without use of RSV vaccine, 14,687 hospitalizations, 11,201 ED encounters, 132,472 PO/HO visits, and 1,230 RSV-related deaths are projected to occur over two years. Pfizer’s RSVpreF would result in a 22,301-case reduction (RSV-H: 2,713; RSV-ED: 2,069; RSV-PO/HO: 17,519) and 227 fewer deaths; total medical care costs would be lower by $86.0M (RSV-H: $64.2M; RSV-ED: $7.4M; RSV-PO/HO: $14.4M) (Table). GSK’s RSVpreF3 would reduce cases by 16,183, deaths by 205, and medical care costs by $76.8M. Moderna’s mRNA-1345 would reduce cases by 9,357, deaths by 112, and medical care costs by $43.2M (based on single-season efficacy data). Conclusion RSV vaccines have the potential to substantially reduce the clinical and economic burden of RSV-LRTI in older adults. Of the three vaccines, Pfizer’s RSVpreF would provide the greatest benefit due to its high 2-year efficacy. Disclosures Ahuva Averin, MPP, Pfizer Inc: Advisor/Consultant Reiko Sato, PhD, Pfizer Inc: employee|Pfizer Inc: Stocks/Bonds (Private Company) Erica Chilson, PharmD, Pfizer Inc: Employee|Pfizer Inc: Stocks/Bonds (Public Company) Mark Atwood, MS, Pfizer Inc: Advisor/Consultant Erin Quinn, BS, Pfizer Inc: Advisor/Consultant

P-1921. Risk Factors for Hospitalization due to COVID-19 in the Current Era of the Pandemic

Abstract Background Certain risk factors place SARS-COV-2 infected individuals at a higher risk of hospitalization and death. While increased vaccination rates and herd immunity have decreased the overall risk of hospitalization and death from COVID-19, some groups of patients may still be at significant risk of morbidity and mortality from COVID-19. However, this population has not been well-described. This study sought to understand the current landscape of patients hospitalized due to COVID-19 to gauge who would most benefit from pre-exposure prophylaxis and other therapies for COVID-19.Table 1:Demographics.Demographics of patients admitted to hospital due to COVID-19.*Immunosuppression defined as having at least one of the following: hematologic malignancy, solid organ transplant, bone marrow transplant, metastatic cancer, asplenia, HIV with CD4 count < 200, other immunosuppressive disease with impaired humoral or cell-mediated immunity, or immunosuppressive medication including corticosteroids (prednisone ≥ 2mg/kg/day or ≥ 20 mg/day or equivalent dose of other corticosteroid) for > 14 days, chemotherapy within past 3 months, calcineurin inhibitor, anti-proliferative agent, mTOR inhibitor, B-cell or T-cell depleting medication, or TNF-alpha inhibitor. Methods This was a retrospective study of adults admitted to a single center for a COVID-19-related reason from August 4, 2023, through February 5, 2024. All admitted patients with a positive SARS-CoV-2 test were identified; patients who were admitted for a non-COVID-19 related reason were excluded from manual chart review. Patient demographic information, vaccination status, risk factors, symptoms, hospital course, and treatment interventions were collected. These data were then analyzed and descriptively characterized.Table 2:OutcomesClinical outcomes of patients admitted to hospital due to COVID-19. Results Of the 408 patients identified who were hospitalized for a COVID-19-related reason during the study period, the median age was 70 years (IQR 60 – 81) with a median length of stay of 5 days (IQR 3-8). Only 13% of patients were up to date on their COVID-19 vaccination at their time of admission (Table 1). Admitted patients had a median of 3 (IQR 2 – 4) risk factors for severe infection, and 26.5% of patients were noted to be immunosuppressed (Table 1). Nearly half of all patients did not require supplemental oxygen during their stay (47%); 38% required only low flow nasal cannula (Table 2). There was a 7.8% 90-day mortality rate. Conclusion These data suggest that most admitted patients in the current COVID-19 era have multiple risk factors and are under-vaccinated. This high-risk population may benefit from updated vaccination, pre-exposure prophylaxis, and/or other therapies to reduce the morbidity from COVID-19. Disclosures Kathleen Degnan, MD, Gilead: Grant/Research Support Amanda Binkley, PharmD, BCIDP, AAHIVP, Viiv: Advisor/Consultant

P-1965. Non-Pharmaceutical Interventions and Protection Against SARS-CoV-2 Infection in a Changing Pandemic Landscape

Abstract Background Non-pharmaceutical interventions (NPI), such as social distancing measures and the use of face masks, are presumed to lower the transmission of SARS-CoV-2. Guidance and mandates by public health authorities, however, have varied throughout the COVID-19 pandemic. This study sought to assess, on a population level, whether self-reported NPI measures were associated with the risk of SARS-CoV-2 infection at different times in the pandemic.Figure 1.Study data collection in relation to COVID-19 cases and pandemic milestone events in California in 2020-2022. The black solid line depicts newly reported COVID-19 cases in California across time. The grey shaded areas show the duration of the first and second shelter-in-place orders in California. The yellow shaded areas show the duration of the regional mask mandates in California. The light blue bars illustrate the cumulative weekly vaccination percentage across time. The red horizontal bars depict when CA-FACTS surveys were conducted. WHO; World Health Organization, CA; California. Methods We conducted a repeated cross-sectional study among randomly sampled households in 3 Northern California counties over 3 time points: Oct 2020-Mar 2021 (wave 1), Oct 2021-Feb 2022 (wave 2) and Mar-Jun 2022 (follow-up survey of wave 2 participants) (Figure 1). Social distancing, face mask use, vaccination status and self-reported COVID-19 were recorded by participants’ response in an online survey. We describe changes in NPI adoption across time and estimate the association of NPI and risk of COVID-19 infection among vaccinated individuals using logistic regression. Results The proportion of participants who reported never or rarely participating in social activities outside their household decreased from 60.2% in wave 1 to 20.5% in the follow-up survey. Similarly, face mask use decreased over time with 91.7% of wave 1 and 92.5% of wave 2 participants reporting consistently wearing a face mask in indoor public spaces compared to 66.4% of follow-up participants (Table 1). In multivariable regression models, social distancing was associated with significantly reduced odds of COVID-19 among vaccinated individuals in both surveys (wave 2 aOR 0.53, 95%CI 0.33-0.81; follow-up aOR 0.20, 95%CI 0.08-0.40). Consistent use of face masks tended to be less in those with self-reported COVID-19 in wave 2 (adjusted odds ratio (aOR) 0.58, 95%CI 0.32-1.13) but showed little impact in the follow-up survey (aOR 0.96, 95%CI 0.65-1.44, Table 2). Conclusion Declines in protection offered by face masking coincided with the lifting of mask mandates and decreased adherence to face mask use in communities overall. In contrast, the importance of social distancing as a protective strategy against COVID-19 infection appeared to increase over time. NPI, particularly social distancing, should remain first-line approaches to preventing infection in future outbreaks. Disclosures All Authors: No reported disclosures

P-2044. Analysis of Post COVID-19 Condition After Ensitrelvir Treatment in Asymptomatic or Mild-Symptoms Only Patients in the SCORPIO Phase2b/3 Study

Abstract Background Ensitrelvir is an oral SARS-CoV-2 3CL protease inhibitor developed to treat COVID-19. In the Phase3 SCORPIO-SR trial targeting mild/moderate COVID-19 patients, the proportion of patients who experienced Post COVID-19 Condition (PCC) until Day 337 was lower in ensitrelvir groups than in placebo group [A. Fukushi et al. The Ninth ESWI Influenza Conference]. Here we report the effect of ensitrelvir on PCC in less symptomatic patients enrolled in another part, Phase2b/3. Proportion of patients with Post-COVID-19 Condition (PCC) and risk reduction versus placebo. Eligible patients were randomized (1:1:1) to orally receive once-daily ensitrelvir 125 mg (375 mg on Day 1), 250 mg (750 mg on Day 1), or placebo for 5 days. The number of patients with mild COVID-19 symptoms was 350 and the number of asymptomatic participants was 34. Among asymptomatic participants (9 in ensitrelvir 125mg, 13 in ensitrelvir 250mg, and 12 in placebo group), 2 participants had PCC (one in 125 mg and the other is placebo group). Data are summarized for patients who completed the PCC questionnaire for at least one timepoint in the intention-to-treat population. a Stuffy nose, runny nose, sore throat, shortness of breath, cough, low energy or tiredness, muscle or body aches, headache, chills or shivering, feeling hot or feverish, nausea, vomiting, diarrhea, loss of smell, loss of taste, muscle weakness, hair loss, palpitations, joint pain, decreased appetite, dizziness, chest pain, skin rash, difficulty with concentration and thinking, difficulty in reasoning and solving problems, memory loss, or insomnia. b Difficulty with concentration and thinking, difficulty in reasoning and solving problems, memory loss, or insomnia. Methods This multinational, multicenter, randomized, double-blind, placebo-controlled study was conducted in 2022 when the Omicron-variant was dominant. Individuals with confirmed SARS-CoV-2 infection, regardless of their vaccination status or risk factors for severe disease, were enrolled. This study targeted patients with diagnosis of COVID-19 asymptomatic/mild symptoms who were screened but not enrolled in Phase3 SCORPIO-SR study. Participants were randomized to either ensitrelvir 125 mg, 250 mg, or placebo. PCC was defined as a condition reported as “not returned to pre-COVID health” with at least one mild/more severe symptom among prespecified 27 symptoms on Day 85, 169, and 337. Investigators and patients remained blinded to drug assignment up to Day 337. Results In total, 124 ,129 ,131 patients were assessed in the ensitrelvir 125 mg, 250 mg, and placebo groups, respectively (mean age, 38.8–41.6 years; men, 51.1–61.2%; 89.9–93.1% had vaccination history). Proportion of patients with PCC on Day 337 for any of the 27 symptoms was 3.5%, 3.4% and 8.8% in ensitrelvir 125 mg, 250 mg and placebo groups, respectively. Ensitrelvir 125 mg and 250 mg showed 60.5% and 61.1% risk reductions versus placebo, respectively. For any of the 4 neurological symptoms, proportion of patients with PCC on Day 337 was 1.7%, 2.6% and 6.4% in ensitrelvir 125 mg, 250 mg and placebo groups, respectively. Risk reductions versus placebo were 72.8% and 59.9% in ensitrelvir 125 mg and 250 mg, respectively (Figure). Conclusion It is suggested that ensitrelvir treatment may reduce PCC in this limited subpopulation with asymptomatic/mild disease. Disclosures Takumi Imamura, M.Math, Shionogi & Co., Ltd.: Stocks/Bonds (Private Company) Hiroshi Yotsuyanagi, MD PhD, Japanese Society of Infectious Disease: President|Shionogi & Co., Ltd.: Board Member|Shionogi & Co., Ltd.: Lecture fees, travel and meeting support, and Chairs in sponsored symposiums|ViiV Healthcare: Lecture fees; Chairs in sponsored symposiums Yohei Doi, MD, PhD, bioMerieux: Lecture fees|Entasis: Grant/Research Support|Fujifilm: Advisor/Consultant|Gilead Sciences: Advisor/Consultant|GSK: Advisor/Consultant|KANTO CHEMICAL CO.,INC.: Grant/Research Support|KANTO CHEMICAL CO.,INC.: Patent for genotyping kit|MeijiSeika Pharma: Advisor/Consultant|Moderna: Advisor/Consultant|MSD: Lecture fees|Pfizer: Advisor/Consultant|Shionogi & Co., Ltd.: Grant/Research Support|Shionogi & Co., Ltd.: Lecture fees Masaya Yamato, MD, PhD, Shionogi & Co., Ltd.: Lecture fees Hiroki Sakaguchi, MA, Shionogi & Co., Ltd.: Stocks/Bonds (Private Company) Hideki Yamanaka, n/a, Shionogi & Co., Ltd.: Stocks/Bonds (Private Company) Ryosuke Imaoka, n/a, Shionogi & Co., Ltd.: Stocks/Bonds (Private Company) Akimasa Fukushi, n/a, Shionogi & Co., Ltd.: Stocks/Bonds (Private Company) Genki Ichihashi, MA, Shionogi & Co., Ltd.: Stocks/Bonds (Private Company) Yuko Tsuge, MSc, Shionogi & Co., Ltd.: Stocks/Bonds (Private Company) Takeki Uehara, Ph.D., Shionogi & Co., Ltd.: Stocks/Bonds (Private Company) Hiroshi Mukae, M.D., Ph.D., AstraZeneca: Lecture fees|Gilead Sciences: Lecture fees|GSK: Lecture fees|MSD: Advisor/Consultant|MSD: Lecture fees|Pfizer: Lecture fees|Shionogi & Co., Ltd.: Advisor/Consultant|Shionogi & Co., Ltd.: Grant/Research Support|Shionogi & Co., Ltd.: Lecture fees

P-1160. Surge of Pediatric Streptococcus pneumoniae Infections at a Tertiary Healthcare Center after Introduction of 15 and 20 Valent Pneumococcal Conjugate Vaccines: Early Evidence of Serotype Replacement?

Abstract Background Routine pneumococcal vaccination has contributed to the overall decrease in pediatric cases of invasive pneumococcal disease (IPD). However, there has been an increase in non-vaccine serotypes (NVT) causing IPD in North America, Europe, and Australia. We describe hospital admissions of Streptococcus pneumoniae-related illness at a tertiary health care center from 2022-2024. Methods Retrospective chart review was conducted of IPD and non-IPD cases admitted to the Children’s Hospital of Georgia from April 2022-April 2023 and April 2023-April 2024. We used the Centers for Disease Control and Prevention (CDC) definition of IPD. IPD and non-IPD disease cases were analyzed for site of infection, concomitant viral infections, vaccination status, Pediatric Intensive Care Unit (PICU) admission, and death. Results From 2023-2024, there were 12 cases of IPD, 8 had bacteremia, 3 had meningitis and bacteremia, and 1 had meningitis compared to only 3 IPD cases in 2022-2023, all with bacteremia. 7 of the 12 cases (58%) of IPD cases in 2023-2024 were fully PCV13 vaccinated compared to 1 of the 3 cases (33%) in 2022-2023. Only RSV and rhino/enterovirus were found concomitantly. 7 patients required PICU admission in 2023-2024, 1 on 2022-2023. 1 patient died during 2023-2024. 2 cases had serotyping during 2023-2024; one had serotype 38 and the other had serotype 10A. PCV20 includes serotype 10A. None of the above serotypes are included in the PCV 13 or PCV 15 vaccines. From 2023-2024, there were 9 cases of non-IPD infection compared to 13 cases in 2022-2023, all of which had pneumonia as the site of infection. Only 5 cases were fully immunized in 2023-2024 while 8 were vaccinated in 2022-2023. Concurrent viruses included parainfluenza, human metapneumovirus, SARS-CoV-2, coronavirus OC43, adenovirus, and rhinovirus. 4 patients required PICU admission in 2023-2024 and 5 in 2022-2023. 1 case died during 2023-2024, and 1 died during 2022-2023. Conclusion The recent surge in IPD cases at our institution could be related to early serotype replacement following vaccine-expanded serotypes since more children with IPD were immunized during the 2023-2024 period. Increased surveillance and serotyping will guide decisions about increased IPD infections. Immunization efforts need to be reinforced in our community. Disclosures All Authors: No reported disclosures

P-1942. Unexpected Cardiac Deaths in Patients with COVID-19 Infection

Abstract Background There are contradictory reports regarding the association of COVID-19 with sudden cardiac deaths. It is unclear whether these deaths are the result of known cardiac disease and risk factors or are unexpected based on prevalent risk factors. Our aim was to determine the association between COVID-19 infection and UCD among individuals who died of a cardiac cause in Qatar. Study Flowsheet Methods All deaths in Qatar in adults >18 years old with any cardiac cause listed as the primary or immediate cause of death were individually reviewed to determine whether the death was unexpected based on the individual’s clinical risk profile. For each case of validated UCD, up to 5 controls with a non-cardiac primary cause of death were identified, matched on age groups, sex, nationality, number of coexisting conditions, and vaccine doses to individuals who died of non-cardiac causes in the same calendar month. Adjusted odds ratios (aOR) comparing odds of prior COVID-19 infection in cases relative to controls were estimated using conditional logistic regression. Association between prior COVID-19 infection and incidence of Unexpected Cardiac Deaths (UCD) in the matched cohorts. Results Among a total of 10,541 deaths, we matched 326 UCD cases to 604 controls with a non-cardiac cause of death. The median age was 48 years for cases and 49 years for controls, 87% were male, and 18% of cases and 20% of controls were Qatari nationals. Approximately three-quarters in each group had no documented comorbidities, and approximately two-thirds were unvaccinated. Prior COVID-19 infection was not associated with a higher risk of UCD (aOR 0.74, 95% CI 0.48, 1.13). No association was observed between prior COVID-19 and UCD in subgroup analyses by age groups, or vaccination status. Qatari nationals, females, and those with > 4 comorbidities were less likely to experience UCD associated with prior COVID-19. Conclusion COVID-19 is not associated with an increased risk of UCD. The observed cardiac deaths are more likely due to the underlying risk profile of the decedents. Disclosures Adeel A. Butt, MD, MS, Gilead Sciences: Grant/Research Support

P-1947. Risk of Severe COVID-19 Reinfection among Persons Hospitalized with a Primary COVID-19 Infection, Minneapolis-St. Paul, Minnesota

Abstract Background SARS CoV-2 continues to circulate broadly making it important to understand risk factors for severe illness when reinfection occurs. We used CDC COVID-19 Hospitalization Surveillance Network (COVID-NET) data to assess reinfection, hospitalization at reinfection (hospitalized reinfection) and ICU admission at reinfection (ICU reinfection) by underlying medical conditions and ICU admission at primary infection. Methods Nonpregnant adults hospitalized 3/9/2020 - 9/30/2021 were identified through COVID-NET, surveillance that includes Minneapolis-St. Paul metropolitan area residents with a positive SARS-CoV-2 result during or ≤ 14 days before admission. Cases were matched to all reports of persons positive for SARS-CoV-2 to identify reinfections, defined as a positive SARS-CoV-2 test > 90 days after the initial positive result through 4/17/2024. Logistic regression was used to assess reinfection and severity of reinfection adjusted for age, sex, race/ethnicity, and vaccination status (aOR). Results 6,434 hospitalized persons met the COVID-NET case definition for their primary infection; 1,189 (18%) had a reinfection. 356 (30%) of the reinfection cases were hospitalized and 51 (14%) of those hospitalized had ICU admission. Having any underlying condition was associated with reinfection (aOR 1.62, 95% CI 1.18, 2.23) and hospitalized reinfection (aOR 2.16, 95% CI 1.27, 3.69). Cardiovascular disease was associated with reinfection (aOR 1.72, 95% CI 1.28, 2.31). Cardiovascular disease (aOR 3.03, 95% CI 1.87, 4.90), blood disorders (aOR 2.42, 95% CI 1.03, 5.37), and renal disease (aOR 1.85, 95% CI 1.12, 3.06) were associated with hospitalized reinfection. All 51 ICU reinfections and 14 reinfection deaths had an underlying condition. Primary ICU admission was not associated with reinfection or hospitalized reinfection but was associated with ICU reinfection (aOR 5.26, 95% CI 1.65, 16.73). Conclusion Among patients hospitalized with COVID-19, underlying conditions and primary ICU admission were associated with severe outcomes during reinfection. These results highlight the continued importance of prevention strategies like vaccination and treatment to mitigate severe illness among patients at highest risk. Disclosures All Authors: No reported disclosures

P-1985. Effect of vaccination on long COVID risk: An analysis of 3.6 million older US adults

Abstract Background Long COVID is a disabling condition that can develop after a SARS-CoV-2 infection. There is limited population-based evidence on the risk of long COVID and the potential protective effects of vaccination, especially among older adults. Our objective was to quantify the association between vaccination status and long COVID risk in older adults using a very large sample of older US adults. Methods We conducted a cohort study of Medicare beneficiaries with COVID-19 (index date) between Oct 1, 2021 and Mar 31, 2023. Community living beneficiaries ≥66 years old, enrolled in Medicare fee-for-service (FFS) were included. Over one year of followup, we measured long COVID diagnoses (U09.9) in the Medicare Part A/ B claims. Individuals who died or disenrolled were censored. Baseline demographics, comorbidities, prior COVID-19 diagnoses, and number of vaccines were measured as of the index date. Cox proportional hazards estimated cause-specific relative rates of long COVID and Fine & Gray competing risk regression estimated absolute risk. Results We identified 3,588,671 eligible Medicare beneficiaries (mean age=76.3; 58% women; 4.6% Black; 12.2% prior COVID-19 diagnosis). A total of 3.2% of beneficiaries were diagnosed with long COVID over follow-up. The adjusted risk of long COVID was higher among beneficiaries with no prior vaccines (4.3%) and lowest among those with four or more prior vaccines (2.5%). The relative rate of long COVID decreased with each vaccine compared to no vaccination (one vaccine adjusted hazard ratio [aHR] = 0.73, 95% confidence interval [CI] = 0.72-0.74; 2 vaccines aHR=0.72, 95%CI=0.71-0.74; 3 vaccines aHR=0.67, 95%CI=0.66-0.68; ≥4 vaccines aHR=0.60, 95%CI=0.59-0.61). Conclusion The risk of long COVID was very low in US Medicare beneficiaries diagnosed with COVID-19, likely due to underreporting and undercoding. Despite low coding rates of long COVID in Medicare claims, a significant dose-response relationship was observed with the number of prior COVID-19 vaccines and reduced risk of long COVID. Efforts to improve the clinical detection and documentation of long COVID in administrative databases will be important for public health surveillance, and vaccinations represent an effective strategy at mitigating long COVID risk in older adults. Disclosures Yasin Abul, MD, Moderna: Grant/Research Support|Moderna, Abt, CDC: Grant/Research Support Daniel Harris, PhD, MPH, Sanofi Vaccines: Advisor/Consultant Kaley Hayes, PharmD, PhD, Genentech: Grant/Research Support|GlaxoSmithKline: Grant/Research Support|Sanofi: Grant/Research Support Vincent Mor, Ph.D., naviHealth: Advisor/Consultant Stefan Gravenstein, MD, MPH, CDC: Advisor/Consultant|CDC: Grant/Research Support|Genentech: Advisor/Consultant|Genentech: Grant/Research Support|Genentech: Honoraria|GlaxoSmithKline: Advisor/Consultant|GlaxoSmithKline: Grant/Research Support|GlaxoSmithKline: Honoraria|Janssen: Advisor/Consultant|Janssen: Grant/Research Support|Janssen: Honoraria|Moderna: Advisor/Consultant|Moderna: Grant/Research Support|Moderna: Honoraria|NIH: Grant/Research Support|Pfizer: Advisor/Consultant|Pfizer: Grant/Research Support|Pfizer: Honoraria|Sanofi: Advisor/Consultant|Sanofi: Grant/Research Support|Sanofi: Honoraria|Seqirus: Advisor/Consultant

P-1961. Epidemiologic analysis of an alpha variant COVID-19 nosocomial cluster that occurred after completed vaccination of healthcare workers

Abstract Background In a field where few reports have been made on the efficacy of SARS-CoV-2 vaccines in healthcare settings. We experienced an outbreak of an alpha variant in a medical institution cluster after healthcare workers were vaccinated, providing a novel perspective on the topic.Figure 1.Epidemic curve based on the day of positive SARS-CoV-2 PCR test (A) or on the symptom onset day (B) during this COVID-19 outbreak The index case was a patient admitted to the hospital on 24 May. The last positive case was detected ten days after the first detection, but 42 patients, including five asymptomatics and three healthcare workers, including an asymptomatic, were infected. Methods We conducted descriptive epidemiology from case detection in the cluster of medical institutions with the alpha variant in June 2021. We also compared the relationship between vaccination status and infection using the Fisher exact test for healthcare workers in the same period.Figure 2.Diagram of hospital room layouts for patients infected in the first wave (through June 1) We confirmed infected inpatients in a wide range of hospital rooms. Results We identified one healthcare worker as a first test-positive case on 4 Jun 2021, and 21 positive patients were identified by screening on the day of detection and the following day. Based on the descriptive epidemiological analysis, the index case was a patient admitted to the hospital on 24 May with pneumonia treated with NPPV in an independently air-conditioned negative pressure room from the third day of admission. The last positive case was detected 10 days after first detection, but 42 patients and three healthcare workers were infected (Figure 1). Forty-two of 88 hospitalized patients (53.7%) and 3 of 38 healthcare workers (7.9%) were infected. There were no cases of infection among the 30 healthcare workers who had completed the 2-dose vaccination, and the infection rate was significantly lower than that of the staff members who had not completed the vaccination (0% (0/30) vs. 37.5% (3/8), p=0.008). No hospitalized patients had completed the 2-dose vaccination, including infected and uninfected cases. Aerosol transmission from initial cases, the patient-to-patient droplet route, and the hospital ward contact route were considered factors in the spread of the disease (Figure 2 and Figure 3).Figure 3.Links within the cluster Aerosol transmission from initial cases, the patient-to-patient droplet route, and the hospital ward contact route were considered factors in the spread of the disease. Conclusion Our study not only underscores the importance of strict adherence to standard precautions, early detection of infected cases, and implementation of route-specific prophylaxis but also highlights the crucial role of vaccination in preventing the outbreak and spread of COVID-19 clusters in medical institutions. Disclosures All Authors: No reported disclosures