Viral illness and neonatal outcomes in neonates exposed to in utero respiratory syncytial virus vaccination vs postnatal nirsevimab.

Relationship between Measures of Neonatal Glycemia, Neonatal Illness, and 2-Year Outcomes in Very Preterm Infants

Respiratory syncytial virus (RSV) is a major cause of serious acute lower respiratory tract infection in infants and the elderly. The lack of a licensed RSV vaccine calls for the development of vaccines with other targets and vaccination strategies. Here, we construct a recombinant protein, designated P-KFD1, comprising RSV phosphoprotein (P) and the E.-coli-K12-strain-derived flagellin variant KFD1. Intranasal immunization with P-KFD1 inhibits RSV replication in the upper and lower respiratory tract and protects mice against lung disease without vaccine-enhanced disease (VED). The P-specific CD4+ Tcells provoked by P-KFD1 intranasal (i.n.) immunization either reside in or migrate to the respiratory tract and mediate protection against RSV infection. Single-cell RNA sequencing (scRNA-seq) and carboxyfluorescein succinimidyl ester (CFSE)-labeled cell transfer further characterize the Th1 and Th17 responses induced by P-KFD1. Finally, we find that anti-viral protection depends on either interferon-γ (IFN-γ) or interleukin-17A (IL-17A). Collectively, P-KFD1 is a promising safe and effective mucosal vaccine candidate for the prevention of RSV infection.

Expression patterns of atopic eczema and respiratory illnesses in a high-risk birth cohort

Alterations in Pulmonary Function Following Respiratory Viral Infection

Viral respiratory tract infections and asthma: The course ahead

This review evaluates the efficacy and safety of novel respiratory syncytial virus (RSV) vaccines approved for adults aged 60 years and older. A literature search through February 27, 2024 was conducted using search terms, such as RSV, viral respiratory illness, vaccine, RSVpreF, RSVpreF3, Prefusion F, Abrysvo, and Arexvy. Data from primary literature and vaccine prescribing information were reviewed, encompassing evaluations of clinical pharmacology, efficacy, safety, adverse events, warnings, and precautions. The literature review process resulted in 10 articles included within this article's scope, including the results of 2 major phase III trials presented in detail. Two RSV vaccines, Respiratory Syncytial Virus Vaccine (recombinant [adjuvanted]; RSVpreF3-ASO1E, Arexvy) and Respiratory Syncytial Virus Vaccine (recombinant; RSVpreF, Abrysvo), approved for preventing RSV-associated lower respiratory tract disease (LRTD) in adults aged 60 years or older in the United States are discussed. Results from Phase III trials have demonstrated the efficacy of 1 dose of these vaccines in preventing RSV-associated LRTD across 2 RSV seasons. The Advisory Committee on Immunization Practices currently recommends use of these vaccines under shared clinical decision-making for adults aged 60 years or older. Most common adverse effects include injection site reactions (eg, site pain, redness, and swelling). Administration requires a single intramuscular injection of 0.5 mL, reconstituted prior to administration. The RSVpreF3-ASO1E and RSVpreF vaccines effectively prevent RSV-associated LRTD in adults aged 60 years and older.

Maternal respiratory syncytial virus (RSV) and pertussis vaccinations are recommended in some countries. While Tdap is widely used in pregnant women, DTaP is the approved pertussis vaccine in Japan. This study aimed to evaluate the safety of maternal RSV and DTaP vaccination, including reactogenicity and pregnancy and neonatal outcomes. This observational study included pregnant women vaccinated with RSV or DTaP. Reactogenicity and health-related quality of life were assessed daily. Pregnancy and neonatal outcomes, including preterm delivery, hypertensive disorder of pregnancy (HDP), cesarean section, low birth weight and NICU admission, were compared with an unvaccinated historical cohort. A total of 252 RSV-vaccinated and 159 DTaP-vaccinated pregnant women were included. Twin pregnancy occurred in 13.9%, 7.4%, and 6.6% of the RSV-vaccinated, DTaP-vaccinated, and unvaccinated cohorts. Grade 1–2 local adverse events occurred in 108 (46.1%) RSV-vaccinated and 102 (75.0%) DTaP-vaccinated women (p < .001), whereas grade 1–2 systemic adverse events occurred in 133 (56.8%) and 61 (44.8%) women (p = .031), respectively. None of the adjusted odds ratios for preterm delivery, HDP, cesarean section, low birth weight, or NICU admission were increased in the RSV-vaccinated and DTaP-vaccinated groups, compared with the unvaccinated group. Maternal RSV and DTaP vaccinations were well tolerated and not associated with increased risks of adverse pregnancy or neonatal outcomes. These findings support broader implementation of maternal vaccination in populations with high twin pregnancy rates.

BackgroundRespiratory syncytial virus (RSV) vaccines were approved in 2023 and recommended for adults over the age of 75 and adults aged 60 – 74 at high risk of severe RSV infection. In this study, we investigated nationwide RSV vaccine administration and the efficacy of RSV vaccines in adults aged over 60.Figure 1.Monthly RSV vaccinations and testing volumes in adults 60 - 74 years of age and in adults 75+ from September 2022 to December 2024. Gray bars and the left y-axis indicate RSV testing volumes. Orange bars and right y-axis indicate RSV vaccination volumes.Figure 2.RSV testing volumes normalized to all respiratory panel testing volumes in December of 2022 – 2024 in adults 60 – 74 years of age and in adults 75+MethodsWe conducted an observational analysis of two nationwide, deidentified crossover datasets of 107,035 RSV vaccination events from September 2023 to December 2024 and 6,660 RSV diagnostic testing from September 2022 to December 2024 in adults over the age of 60 who were administered seasonal vaccinations. Time-to-event analysis was conducted for 110 adults over age 60 with RSV diagnostic testing performed at Labcorp within one year of vaccination.Figure 3.Monthly RSV positivity rates and vaccination volumes in adults 60 – 74 years of age and in adults 75+ from September 2022 to December 2024. Line plot indicates RSV positivity rates. Orange bars and right y-axis indicate RSV vaccination volumes. Shapes indicate the number of diagnostic tests performed per month.Figure 4.RSV diagnostic testing results within one year of RSV vaccination in 57 adults o60 – 74 years of age and in 53 adults 75+. Bars are colored by when each patient received the RSV vaccine.ResultsPeak uptake of RSV vaccines occurred in November 2023 in the 2023 – 2024 RSV vaccination season and in October 2024 in the 2024 – 2025 RSV vaccination season in adults aged 60 – 74. For adults 75+, peak vaccine uptake occurred in November 2023 and October 2024 (Fig 1). Peak RSV testing in adults aged 60 – 74 occurred in December. Peak RSV testing in adults 75+ occurred in December 2022 and in January and December 2024. Peak uptake of RSV vaccines occurred 1 – 2 months prior to the peak RSV testing months. Testing volumes in peak testing month of December decreased by 43.8% in adults aged 60 – 74 and by 42.5% in adults 75+ 2024 from 2023 (Fig 2). Peak RSV positivity rates in 2023 – 2024 RSV vaccination season occurred in December in adults aged 60 – 74 (9.3%) and adults aged 75+ (7.4%; Fig 3). Vaccine uptake peaked 1 – 2 months prior to peak RSV positive months. There were no breakthrough RSV infections in 57 adults aged 60 – 74 or in 53 adults aged 75+ with RSV diagnostic testing within one year of vaccination (Fig 4).ConclusionOur data demonstrate a potential correlation between the introduction of RSV vaccines and a reduction in RSV diagnostic testing in older adults. Furthermore, our data suggests that RSV vaccination is highly protective for RSV infection with zero breakthrough infections in a limited dataset. Further longitudinal study is warranted.DisclosuresKathryn Lang, MD, PhD, VaxCare: Advisor/Consultant David Alfego, PhD, Labcorp: Employee|Labcorp: Employee|Labcorp: Stocks/Bonds (Public Company) Min Kyung Lee, PhD, Labcorp: Employee|Labcorp: Stocks/Bonds (Public Company) Laura Gillim, PhD, Labcorp: Stocks/Bonds (Public Company) Charles M. Walworth, MD, Labcorp: Employee|Labcorp: Stocks/Bonds (Public Company)|Labcorp: Stocks/Bonds (Public Company) Suzanne Dale, PhD, Labcorp: Stocks/Bonds (Public Company) Colm Smart, MBA, VaXcare: Stocks/Bonds (Private Company) Ruth Carrico, PhD, DNP, APRN, VaxCare: Advisor/Consultant Payman Ghasemi, PhD, VaxCare: Grant/Research Support

Maternal listeriosis is uncommon but clinically important due to the risk of severe maternal illness and adverse perinatal outcomes. Nonspecific symptoms often overlap with viral and respiratory illnesses, delaying diagnosis. We describe the case of a 28-year-old gravida 4 para 2+1 at 29+5 weeks who presented with fever, frontal headache, photophobia, and generalized myalgias. Significant medical history included asthma, chronic hypertension, chronic hepatitis B and C carriage, and a sickle cell variant. Blood cultures grew Listeria monocytogenes. She was treated with intravenous amoxicillin and gentamicin after initial empiric therapy. Despite concern for central nervous system involvement, brain MRI revealed no intracranial pathology. She transitioned to benzylpenicillin for outpatient therapy and achieved complete recovery. A healthy infant was delivered by emergency caesarean section at 39+1 weeks. Maternal listeriosis can closely mimic common viral illnesses. Thus, maintaining a high index of suspicion, especially in pregnant women with nonspecific febrile symptoms, can facilitate timely diagnosis and treatment, which is essential to optimising maternal and neonatal outcomes.

Vaccines have an important role in reducing antibiotic prescribing. Population-based estimates of antibiotic prescribing for acute viral respiratory illness among high-risk populations are needed to inform vaccine policy-making. Our objective was to derive population-based estimates of seasonal outpatient antibiotic prescriptions among high-risk adults with respiratory syncytial virus (RSV), influenza, or human metapneumovirus (hMPV) illness. We included adults with laboratory-confirmed medically attended RSV, influenza, or hMPV illness and ≥1 high-risk condition enrolled in the US Flu VE Network in central and northern Wisconsin, 2015-16 to 2019-20. We extracted data on outpatient antibiotics prescribed ≤7 days of enrolment. We estimated the seasonal number of antibiotic prescriptions associated with each viral illness per 10 000 high-risk adults using Poisson regression and stratification and weighting. We incorporated adjustment factors to account for incomplete overlap between influenza and RSV or hMPV seasons using state respiratory infection surveillance data. 3601 respiratory specimens from high-risk adults were included. 303 (8.4%), 1011 (28%), and 289 (8.0%) tested positive for RSV, influenza, or hMPV, respectively. 106/303 (35%), 174/1011 (17%), and 107/289 (37%) patients received ≥1 antibiotic prescription, respectively. After stratification and weighting, seasonal population-based estimates for the number of antibiotic prescriptions where 29 (95% confidence interval 22-39), 52 (41-65), and 31 (24-40) per 10 000 high-risk adults, respectively. Our results suggest that RSV, influenza, and hMPV illness contribute substantially to antibiotic prescribing among high-risk adults in rural Wisconsin. Understanding the impact of vaccines on antibiotic use and resistance is imperative for assessing their full public health value.

IntroductionThe burden of respiratory syncytial virus (RSV) disease is substantial among adults aged ≥ 60 years and adults with risk factors for severe RSV. This study assessed the knowledge, attitudes, and practices of healthcare professionals (HCPs) related to RSV disease and vaccination, with a focus on adults aged ≥ 60 years.MethodsDuring November 14–30, 2023, a cross-sectional, web-based survey was administered to HCPs, targeting a total of 600 primary care physicians (PCPs), specialist physicians, nurse practitioners (NPs)/physician assistants (PAs), and pharmacists. Survey questions evaluated knowledge about RSV disease, vaccines, and vaccination recommendations; RSV-related attitudes and perceptions; and RSV vaccination practices. Responses were analyzed descriptively, overall and by HCP subgroup. Multivariable logistic regression models were used to explore HCP characteristics associated with RSV vaccination knowledge and practices.ResultsOf the 603 respondents (148 PCPs, 151 specialist physicians, 150 NPs/PAs, and 154 pharmacists), 63.0% were very familiar with RSV disease in patients aged ≥ 60 years. Although most HCPs recognized the benefits of RSV vaccination within this patient population, many HCPs were not fully knowledgeable about RSV vaccine recommendations, and 33.5% had not recommended, prescribed, or administered any RSV vaccine to patients aged ≥ 60 years in the previous 3 months. In multivariable regression analyses, HCP familiarity with RSV disease (among other factors) was consistently associated with RSV vaccination knowledge and practices.ConclusionsThis study characterized RSV disease- and vaccine-related knowledge, attitudes, and practices among HCPs in the United States during the first season of RSV vaccine availability for adults aged ≥ 60 years. These findings can help to inform HCP and patient education efforts to address potential RSV vaccination knowledge gaps and ensure equitable access to RSV vaccines among older adults.Supplementary InformationThe online version contains supplementary material available at 10.1007/s40121-025-01119-0.

A novel kindred with inherited STAT2 deficiency and severe viral illness

Respiratory syncytial virus (RSV) remains one of the most important infectious causes of hospitalization in infants and children. This enveloped, RNA virus produces predictable yearly outbreaks of disease that typically peak between January and February in countries in the northern hemisphere.1 The outcome of RSV infection varies from mild upper respiratory tract infection in approximately 75% of infected infants and young children to severe life-threatening disease in a small percent of infected patients.2 In the United States, RSV lower respiratory tract infection accounts for nearly 50% of hospitalizations due to bronchiolitis and 25% of hospitalizations due to pneumonia.1 Serologic surveys suggest that by 2 years of age, more than 90% of all children have been infected by RSV.3 Whether RSV infection early in life predisposes to subsequent reactive airway disease remains an unanswered question. Reinfection is common, indicating that immunity to RSV following natural infection is less than complete.4-6RSV lower respiratory tract disease occurs primarily in infants under 2 years of age; most infants who require hospitalization are previously healthy infants less than 6 months of age. Premature infants, infants born with congenital heart disease, and those with chronic lung disease (such as bronchopulmonary dysplasia [BPD]) constitute additional high-risk groups with high rates of hospitalization due to RSV infection.7-13 A recent report describes RSV mortality rates among such hospitalized infants of 4% to 5%.14Pre-engraftment bone marrow transplant recipients, solid organ transplant recipients, and lymphopenic children receiving chemotherapy appear to suffer even higher mortality rates, although prospective data are not available.15 Morbidity in these groups is also great; the average hospital stay and intensity of care for such children may be several times that of previously healthy infants.Despite the importance of RSV as a pathogen in the pediatric age group, options for treatment and prevention of RSV disease are limited. Aerosolized ribavirin was licensed in 1986 for treatment of children hospitalized with severe RSV lower respiratory tract infection. The efficacy of ribavirin therapy remains controversial despite the growing number of carefully conducted trials.16 Factors that complicate evaluation of antiviral therapy include the self-limited nature of most viral respiratory tract illness, and variation in the natural history of RSV disease from patient to patient. These variables make it difficult to select and define distinct endpoints that can be used to evaluate differences between treatment and control groups.Active immunization to prevent severe RSV disease has not yet been successful. Persistent concern regarding vaccine safety in the young infant is the result of an unanticipated reaction to a formalin inactivated RSV vaccine used in trials conducted in the early 1960s.17-19 Recipients (less than 12 months of age) of the inactivated RSV vaccine experienced higher mortality and morbidity rates upon subsequent RSV infection than did infants who received the control vaccine. The immunologic mechanism for this reaction remains unclear although there appears to have been an aberration in both the cellular and humoral response to the vaccine. Vaccine development is also complicated by the limited ability of infants to mount an immune response to RSV glycoprotein antigens. Furthermore, the presence of maternal neutralizing antibodies may attenuate an active immune response in a vaccinated infant. Despite current efforts to develop subunit vaccines, peptide vaccines, or live attenuated RSV vaccines, it is unlikely that active immunization for infants will be available in the near future.20As an alternative to active immunization against RSV, several approaches to passive immunization in high-risk infants have been evaluated. Clinical trials were first conducted using standard intravenous immune globulin (IGIV). Two randomized controlled trials involving monthly infusions of standard IGIV to high-risk infants failed to demonstrate a reduction in hospitalization rates due to RSV.2122 This lack of efficacy was most likely due to a failure to attain adequate peak and trough RSV neutralizing antibody titers. With the development of an RSV-enriched immune globulin in the late 1980s (RSV-IGIV), it became possible to achieve sufficiently high neutralizing antibody levels in the outpatient setting with infusion of a reasonable fluid volume (15 mL/kg). The first RSV-IGIV prophylaxis trial (National Institute of Allergy and Infectious Disease [NIAID] trial) published in 1993 was conducted over three respiratory virus seasons and included 249 children with prematurity, chronic lung disease or congenital heart disease.23 Children who received 750 mg/kg/dose of RSV-IGIV had a 63% reduction in RSV hospitalizations and a 63% reduction in RSV hospital days relative to control patients receiving no RSV-IGIV. A second prophylaxis trial using RSV-IGIV (PREVENT trial), was conducted over one respiratory virus season and included 510 premature infants with and without BPD.24 This trial demonstrated a 41% reduction in RSV hospitalizations and a 53% reduction in RSV hospital days. A third multicenter RSV-IGIV prophylaxis trial involving 416 infants and children (Cardiac trial) failed to show an overall reduction in RSV disease severity in children with congenital heart disease (unpublished data). A meta-analysis of children less than 6 months of age from all three prophylaxis trials demonstrated a 47% reduction in RSV-induced hospitalization (95% confidence interval of .28–.82) (P = .006) (Table). However, caution must be observed in interpreting these data. Although there is considerable interest in the evaluation of hospitalization rates in subgroups of infants, none of the three trials were prospectively designed for subgroup analysis.Two additional clinical benefits of polyclonal immune globulin administration were observed in recipients of RSV-IGIV prophylaxis. The PREVENT trial demonstrated a 38% reduction in hospitalization due to respiratory tract infection by any respiratory virus and a 46% reduction in total hospital days due to all respiratory illnesses.24 Further, both the NIAID trial and the PREVENT trial demonstrated a reduction in the incidence of acute otitis media in high-dose RSV-IGIV recipients (750 mg/kg/dose) relative to low-dose or control patients.2425RSV-IGIV use in patients with congenital heart disease has been evaluated in two trials (the NIAID trial and the Cardiac trial) and has involved a total of 516 children. The safety of RSV-IGIV, particularly in children with cyanotic heart disease, is uncertain. There appeared to be an increased incidence in both morbidity and mortality, particularly in association with cardiac surgery in RSV-IGIV recipients with cyanotic heart disease as compared with placebo recipients. The deaths occurred at variable times, up to 3 months following an RSV-IGIV infusion. No explanation has yet been found. At the present time, use of RSV-IGIV should be avoided in children with cyanotic heart disease. Among children with left to right shunts who received RSV-IGIV there was not a statistically significant reduction in the overall incidence of RSV hospitalization relative to the control group. Therefore, based on the currently available data, RSV-IGIV does not appear to be indicated for most children with noncyanotic congenital heart disease. It may be that immunoprophylaxis will be beneficial in those infants with noncyanotic heart disease who also satisfy immunoprophylaxis criteria based on prematurity or the presence of BPD. The role of RSV-IGIV in infants with large left to right shunts with pulmonary hypertension remains uncertain.RSV-neutralizing antibodies are directed mainly against two surface glycoproteins. The G glycoprotein mediates RSV attachment to a cell that will support RSV replication by binding with cellular receptors containing sialic acid. The F glycoprotein mediates fusion of the viral lipid envelope with the plasma membrane of the cell. Although there may be considerable sequence divergence in the G glycoprotein between RSV subgroups, the important neutralizing epitopes of the F glycoprotein appear to be faithfully conserved between RSV strains and over time. There has been interest in the use of monoclonal antibodies for prophylaxis against RSV disease because of the possibility of intramuscular (rather than intravenous) administration. One immunoprophylaxis trial using a humanized immunoglobulin G (IgG) monoclonal antibody was conducted during the 1995–1996 respiratory season. In this large, multicenter, double-blind, randomized, placebo-controlled trial, monoclonal antibody or placebo was administered intramuscularly once a month to preterm infants during the respiratory virus season. The results proved disappointing (unpublished data). Although safe, this monoclonal antibody preparation did not reduce RSV hospitalization rates at the dose administered. A second multicenter prophylaxis trial using a higher dose of a somewhat different humanized murine IgG monoclonal antibody and involving over 1500 patients is currently underway.RSV transmission occurs primarily by direct introduction of virus contaminated secretions onto mucous membranes of the upper airway. Bronchiolitis and pneumonia develop when RSV from the upper airway is aspirated into the lungs. The presence of RSV immunoglobulin A (IgA) nasal antibody may protect infants against the low titer of RSV that initiates infection. Studies in experimental animals demonstrate that intranasal administration of a murine monoclonal IgA directed against the RSV F glycoprotein significantly reduced viral replication in the nasal turbinates and the lungs.2627 Phase III prophylaxis trials to evaluate topical daily instillation of IgA antibody as nose drops are currently in progress in high-risk infants.The severity of RSV infection appears to be a function of both a direct viral cytopathic effect and the immune response of the host. Evidence supporting the concept that antiviral activity alone may not be sufficient to attenuate RSV disease expression comes from the unpublished trial demonstrating little if any benefit from prophylaxis with monoclonal IgG antibody, and from the clinical trials that show little beneficial effect from RSV-IGIV in the treatment of established RSV disease in infants.28 The beneficial effect on RSV disease severity that is derived from immunoprophylaxis with a hyperimmune polyclonal product may not be due to RSV neutralizing antibody alone.29 What other critical functions might be present in RSV-IGIV that are not present in a preparation of monoclonal antibodies? Recognized immunomodulatory functions of standard IGIV include: alteration of cytokine production,30 inhibition of T-cell proliferation in vitro,31 increase in natural killer cell activity,32 increase in antibody dependent cell cytotoxicity,32 and neutralization of superantigen activity.33 How important these or other as yet unrecognized immunomodulatory functions are in the attenuation of RSV disease expression remains to be determined.The cost of immunoprophylaxis with RSV-IGIV (licensed in 1996 by the Food and Drug Administration and sold under the trade name RespiGam) over one respiratory season is approximately $5000.34Therefore, it is important that prophylaxis be reserved for carefully selected infants. A recently published consensus statement reviewed the existing literature on RSV disease in various high-risk groups and offered the following guidelines for selection of RSV-IGIV eligible patients15:It must be remembered that the majority of children hospitalized due to RSV disease are previously healthy, young infants. During the 1995–1996 respiratory virus season, 69% of 95 children hospitalized at the New England Medical Center with RSV infection were full-term infants with normal cardiac and pulmonary status. Therefore, use of RSV-IGIV in appropriately selected, high-risk infants is unlikely to dramatically reduce the overall number of RSV induced admissions. However, high-risk children have a disproportionately high economic impact on RSV-associated health care costs because of the greater disease severity and the complexity of care required for these groups. In appropriately selected infants for whom the risk of hospitalization due to RSV and other respiratory viruses is greatest, passive immunoprophylaxis should have an important medical impact and improve their quality of life.

The findings of this review suggest that maternal RSV vaccination reduces laboratory-confirmed RSV hospitalisations in infants. There are no safety concerns about intrauterine growth restriction and congenital abnormalities. We must be careful in drawing conclusions about other safety outcomes owing to the low and very low certainty of the evidence. The evidence available to date suggests RSV vaccination may have little or no effect on stillbirth, maternal death, and infant death (although the evidence for infant death is very uncertain). However, there may be a safety signal warranting further investigation related to preterm birth. This is driven by data from one trial, which is not fully published yet. The evidence base would be much improved by more RCTs with substantial sample sizes and well-designed observational studies with long-term follow-up for assessment of safety outcomes. Future studies should aim to use standard outcome measures, collect data on concomitant vaccines, and stratify data by timing of vaccination, gestational age at birth, race, and geographical setting.

BackgroundOn June 26, 2024, the CDC updated respiratory syncytial virus (RSV) vaccine recommendations to a single dose of RSV vaccine for all adults aged ≥ 75 years and adults aged 60-74 years with increased risk of severe RSV disease. Using electronic health record (EHR) data from the VISION platform, we described characteristics of patients testing negative for RSV who did and did not receive an RSV vaccine and assessed factors associated with RSV vaccine receipt.Figure 1:Characteristics associated with receipt of respiratory syncytial virus (RSV) vaccination among test-negative patients with an emergency department (ED) encounter for RSV-like illness (RLI) during the 2024-2025 season in the VISION network, N=23,403 patientsFigure 2:Characteristics associated with receipt of respiratory syncytial virus (RSV) vaccine among test-negative patients with an inpatient encounter for RSV-like illness (RLI) during the 2024-2025 season in the VISION network, N=25,020 patientsMethodsPatients with ≥ 1 emergency department (ED) or inpatient encounter at any of 6 participating health systems in 8 states with RSV-like illness (RLI) during October 1, 2024-March 31, 2025 were included. Vaccination status was ascertained from EHR, state and city immunization information systems, and medical claims. Patients who tested positive for SARS-CoV-2 or influenza viruses at the same RLI encounter were excluded. Patient age, sex, race and ethnicity, Medicaid status, number of underlying medical conditions, month of medical encounter, and documented receipt of COVID-19 or influenza vaccines were evaluated as covariates when assessing the odds of vaccination. The best fitting multivariable logistic regression models using Bayesian Information Criterion were chosen.ResultsAmong 48423 included patients, 2113 (4.4%) had documented RSV vaccine receipt. The odds of RSV vaccination differed by site and increased with calendar time and age. Compared to patients aged 60-64 years, those aged ≥ 75 years were more likely to have received an RSV vaccine (ED: aOR: 3.6, 95%CI: 2.7-4.8, Figure 1; inpatient: aOR: 2.3, 95%CI: 1.7-3.0, Figure 2). Receipt of both influenza and COVID-19 vaccine within the same season had the strongest association with RSV vaccination in both the ED (aOR: 14.88, 95%CI: 11.87-18.89, Figure 1) and hospital setting (aOR: 20.04, 95%CI: 16.20-25.03, Figure 2).ConclusionReceipt of other respiratory viral vaccines was the strongest indicator of RSV vaccination in the 2024-2025 RSV season in patients testing negative for RSV among all demographic and clinical characteristics considered. RSV vaccination was lower among those aged 60-64 years than older patients. These findings inform future methods to estimate vaccine effectiveness and inform policy implementation.DisclosuresGabriela Vazquez-Benitez, PhD, MSc, AbbVie: research funding not related to this study|Sanofi: Grant funding for other research not related to this study Stephanie Irving, MHS, Westat: Grant/Research Support Nicola P. Klein, MD, PhD, AstraZeneca: Grant/Research Support|Centers for Disease Control and Prevention: Grant/Research Support|GlaxoSmithKline: Grant/Research Support|Janssen: Grant/Research Support|Merck: Grant/Research Support|Moderna: Grant/Research Support|Pfizer: Grant/Research Support|Sanofi Pasteur: Grant/Research Support|Seqirus: Grant/Research Support Shaun J. Grannis, MD, MS, Centers for Disease Control and Prevention: Grant/Research Support|National Institutes of Health NCATS: Grant/Research Support|National Institutes of Health NIMH: Grant/Research Support Toan Ong, PhD, Centers for Disease Control and Prevention via Westat: Grant/Research Support|Patent Title: Systems and Methods For Record Linkage: Patent Number: PCT/US2018/047961|PCORI: Travel Support|Regenstrief Institute: Advisor/Consultant|Regenstrief Institute: Travel Support Sarah W. Ball, MPH, ScD, Centers for Disease Control and Prevention, Contract #200-2019-F-06819: Grant/Research Support|Centers for Disease Control and Prevention, Contract #75D30121D12779: Grant/Research Support|Novavax: Grant/Research Support Jingran Cao, MS, Sanofi Pasteur: Grant/Research Support Charlene E. McEvoy, MD, MPH, Astra Zeneca: Grant/Research Support|Centers for Disease Control and Prevention: Grant/Research Support|Department of Defense: Grant/Research Support|GlaxoSmithKline: Grant/Research Support|National Institutes of Health: Grant/Research Support|PCORI: Grant/Research Support Ousseny Zerbo, PhD, Centers for Disease Control and Prevention: Grant/Research Support|Moderna: Grant/Research Support|National Institutes of Health: Grant/Research Support|Pfizer: Grant/Research Support John R. Hansen, MPH, Centers for Disease Control and Prevention: Grant/Research Support Lawrence Block, MPH, MPA, Centers for Disease Control and Prevention: Grant/Research Support Karen B. Jacobson, MD, MPH, Centers for Disease Control and Prevention: Grant/Research Support|National Institutes of Health: Grant/Research Support|Pfizer: Grant/Research Support William F. Fadel, PhD, Centers for Disease Control and Prevention: Grant/Research Support Catia Chavez, MPH, Westat: Grant/Research Support Karthik Natarajan, PhD, Centers for Disease Control and Prevention: Grant/Research Support Ryan E. Wiegand, PhD, Merck & Co., Inc.: Stocks/Bonds (Public Company)|Sanofi S.A.: Stocks/Bonds (Public Company)