Test-negative Case-control Study Research Articles

Effectiveness of inactivated influenza vaccine against laboratory-confirmed influenza among Chinese elderly: a test-negative design

BackgroundEvidence on the effectiveness of influenza vaccination in the elderly is limited, and results are controversial. There are also few reports from China.MethodsWe conducted a test-negative case-control study design to estimate influenza vaccine effectiveness (VE) against laboratory-confirmed influenza-associated visits among elderly (aged ≥ 60 years) across four influenza seasons in Ningbo, China, from 2018 to 19 to 2021-22. Influenza-positive cases and negative controls were randomly matched in a 1:1 ratio according to age, sex, hospital, and date of influenza testing. We used logistic regression models to compare vaccination odds ratios (ORs) in cases to controls. We calculated the VE as [100% × (1-adjusted OR)] and calculated the 95% confidence interval (CI) around the estimate.ResultsA total of 30,630 elderly patients tested for influenza with virus nucleic acid or antigen during the study period. After exclusions, we included 1 825 influenza-positive cases and 1 825 influenza-negative controls. Overall, the adjusted VE for influenza-related visits was 63.5% (95% CI, 56.3–69.5%), but varied by season. Influenza VE was 59.8% (95% CI, 51.5–66.7%) for influenza A and 89.6% (95% CI, 77.1–95.3%) for influenza B. The VE for ages 60–69 and 70–79 was 65.2% (95% CI, 55.4–72.9%) and 69.8% (95% CI, 58.7–77.9%), respectively, but only 45.4% (95% CI, 6.2–68.2%) for ages 80 and over.ConclusionsStandard-dose inactivated influenza vaccine has shown good protection in the elderly in China. However, protection may not be satisfactory in people aged 80 years and older.

Effectiveness of BNT162b2 Vaccine Against Symptomatic SARS-CoV-2 Infection in Children Aged 5-11 Years in Japan During Omicron Variant Predominate Periods.

Although the effectiveness of BNT162b2 messenger RNA vaccines against the Omicron variant has been reported in several countries, data are limited in children living in Asian countries. Therefore, this study aimed to estimate the effectiveness of the pediatric primary two-dose monovalent mRNA vaccine series in preventing symptomatic novel coronavirus disease 2019 (COVID-19) in Japan. We conducted a test-negative case-control study (262 test-positive cases and 259 test-negative controls) in patients aged 5-11 years who presented with COVID-19-like symptoms during the Omicron BA.2- and BA.5-predominant periods. Vaccination status, demographic data, underlying medical conditions, lifestyle, personal protective health behaviors, living environment, and PCR test results were obtained using parent-administered questionnaires and clinical records. Vaccine effectiveness (VE) against symptomatic COVID-19 was calculated using a multivariate logistic regression analysis. Of the test-positive cases and test-negative controls, 9.2% (n = 24) and 12.7% (n = 33) received two vaccine doses, respectively. Having siblings and a BA.5-dominant period were significantly associated with symptomatic COVID-19. After adjusting for age, siblings, study period, and duration after the last vaccination, the overall VE of two-dose vaccination was 50.0% (95% confidence interval [CI], 5-74%). VE was 72% (95% CI, 24-89%) within 3 months after the two-dose vaccination, while it decreased to 24% (95% CI, -80% to 68%) after 3 months. Two BNT162b messenger RNA vaccine doses provided moderate protection against symptomatic COVID-19 during the Omicron variant period. A time-dependent decrease in VE was noted after the second dose; thus, a booster dose 3 months after the second dose is warranted.

Outdoor air pollution as a risk factor for testing positive for SARS-CoV-2: A nationwide test-negative case-control study in the Netherlands

Air pollution is a known risk factor for several diseases, but the extent to which it influences COVID-19 compared to other respiratory diseases remains unclear. We performed a test-negative case-control study among people with COVID-19-compatible symptoms who were tested for SARS-CoV-2 infection, to assess whether their long- and short-term exposure to ambient air pollution (AAP) was associated with testing positive (vs. negative) for SARS-CoV-2. We used individual-level data for all adult residents in the Netherlands who were tested for SARS-CoV-2 between June and November 2020, when only symptomatic people were tested, and modeled ambient concentrations of PM10, PM2.5, NO2 and O3 at geocoded residential addresses. In long-term exposure analysis, we selected individuals who did not change residential address in 2017–2019 (1.7 million tests) and considered the average concentrations of PM10, PM2.5 and NO2 in that period, and different sources of PM (industry, livestock, other agricultural activities, road traffic, other Dutch sources, foreign sources). In short-term exposure analysis, individuals not changing residential address in the two weeks before testing day (2.7 million tests) were included in the analyses, thus considering 1- and 2-week average concentrations of PM10, PM2.5, NO2 and O3 before testing day as exposure. Mixed-effects logistic regression analysis with adjustment for several confounders, including municipality and testing week to account for spatiotemporal variation in viral circulation, was used. Overall, there was no statistically significant effect of long-term exposure to the studied pollutants on the odds of testing positive vs. negative for SARS-CoV-2. However, significant positive associations of long-term exposure to PM10 and PM2.5 from specifically foreign and livestock sources, and to PM10 from other agricultural sources, were observed. Short-term exposure to PM10 (adjusting for NO2) and PM2.5 were also positively associated with increased odds of testing positive for SARS-CoV-2. While these exposures seemed to increase COVID-19 risk relative to other respiratory diseases, the underlying biological mechanisms remain unclear. This study reinforces the need to continue to strive for better air quality to support public health.

BBIBP-CorV vaccine effectiveness against COVID-19 in patients aged 60 years and older during the Delta-dominant period in the Federation of Bosnia and Herzegovina, a test-negative case-control study

COVID-19 vaccine uptake in the Federation of Bosnia and Herzegovina (FBiH) accelerated in the second half of 2021, with greater vaccine availability. In this study, we estimated the vaccine effectiveness (VE) of complete primary series BBIBP-CorV vaccine against COVID-19 in patients aged 60 years and older, during the Delta-dominant period, using a test-negative case-control design. Surveillance sites were 11 primary health care centers (PHC) collecting patient data from October 1, 2021, to January 4, 2022, retrospectively according to a common protocol. In total, we included 1711 participants in the analysis: 933 cases and 778 controls. Of the 933 cases, 508 (54.4 %) had mild and 425 (45.6 %) had moderate to severe disease presentation. We observed no effectiveness against mild COVID-19. Overall vaccine effectiveness was 65.0 % (95 %CI: 40.1–79.5) against moderate to severe COVID-19. In time since vaccination analysis, VE was 78.7 % (95 % CI: 54.8–89.9) in patients who received their last dose < 90 days before onset; 66.0 % (95 % CI: −0.5–88.5) in those 90–119 days before onset; 42.1 % (95 % CI: −88.6–82.3) in those 120–149 days before onset and 45.0 % (95 % CI: −94.0–84.4) in those ≥ 150 days before onset. In our study, two doses of BBIBP-CorV provided considerable protection against moderate to severe COVID-19 in older adults, highest within 3 months after second dose, during the Delta-dominant period. Point estimates declined thereafter, suggesting a need for additional doses.

Effectiveness of the Sanofi/GSK (VidPrevtyn Beta) and Pfizer-BioNTech (Comirnaty Original/Omicron BA.4-5) bivalent vaccines against hospitalisation in England

The Sanofi/GSK AS03-adjuvanted (VidPrevtyn Beta) vaccine and the Pfizer-BioNTech mRNA (Comirnaty Original/Omicron BA.4-5) bivalent vaccine were offered to adults aged 75 years and over in England from 3rd April 2023. This is the first time an adjuvanted COVID-19 vaccine has been administered as part of a UK COVID-19 vaccination programme. In clinical trials, antibody levels generated were comparable with mRNA vaccines but there are no real-world data on the effectiveness or duration of protection. We used a test-negative case-control study design to estimate the incremental vaccine effectiveness of the Sanofi/GSK and Pfizer bivalent BA.4-5 boosters against hospitalisation amongst those aged 75 years and older in England. Cases (those testing positive) and controls (those testing negative) were identified from the national COVID-19 PCR testing data undertaken in hospital settings. The study period included tests from 3rd April 2023 to 27th August 2023. Tests were linked to the COVID-19 vaccination register and to the national hospital admission database, restricting to those with an acute respiratory infection coded in the primary diagnosis field. Vaccine effectiveness was estimated using multivariable logistic regression amongst those who had last received an autumn 2022 booster given at least 3 months prior. The test result was the outcome and vaccination status the exposure. Analyses were adjusted for week of test, gender, age, clinical risk group status, care home resident status, region, index of multiple deprivation, ethnicity, influenza vaccination status and recent COVID-19 positivity. There were 14,169 eligible tests from hospitalised individuals aged 75 years and older; 3005 cases (positive tests) and 11,164 controls (negative tests). Effectiveness was highest in the period 9-13 days post vaccination for both manufacturers at about 50%; 43.7% (95% CI, 20.1-60.3%) and 56.1% (95% CI, 25.2-74.2%) for Sanofi/GSK and Pfizer BA.4-5, respectively. There was evidence of waning with a reduction to about 30% for both manufacturers after 5-9 weeks. The longest time interval post vaccination for which we were able to estimate effectiveness was 10+ weeks post vaccination, at which point vaccine effectiveness was 17.6% (95% CI,-3.6 to 34.5%) and 37.9% (95% CI, 13.2-55.5%) for the Sanofi/GSK and Pfizer BA.4-5 boosters, respectively. Both boosters provided good protection against hospitalisation amongst older adults. The finding that the adjuvanted vaccine targeting the distant Beta strain had similar effectiveness to the bivalent mRNA vaccine targeting more closely matched Omicron sub-lineages is notable and highlights the need for further real-world studies into the effectiveness of vaccines from different vaccine platforms and formulations in the presence of matched and unmatched strains. No external funding.

Keeping university open did not increase the risk of SARS-CoV-2 acquisition: A test negative case-control study among students.

During the SARS-CoV-2 testing program offered through the RT-PCR test by Sapienza University of Rome, we conducted a test-negative case-control study to identify risk factors for acquiring SARS-CoV-2 infection among university students. Each SARS-CoV-2-positive case detected was matched to two controls randomly selected from students who tested negative on the same day. 122 positive students and 244 negative students were enrolled in the study. Multivariable conditional logistic regression models were built. Adjusted odds ratios (aORs) and 95% confidence intervals (CIs) were calculated. A second model was limited to students who had attended campus. Out of 8223 tests for SARS-CoV-2, 173 students tested positive (2.1%), of whom 122 (71.5%) were included in the case-control study. In the first analysis, being a non-Italian student (aOR: 8.93, 95% CI: 2.71-29.41), having received only the primary vaccination course (aOR: 2.94, 95% CI: 1.24-6.96) compared to the booster dose, known exposure to a COVID-19 case or someone with signs/symptoms suggestive of COVID-19 (aOR: 6.51, 95% CI: 3.48-12.18), and visiting discos (aOR: 4.07, 95% CI: 1.52-10.90) in the two weeks before testing increased the likelihood of SARS-CoV-2 infection. Conversely, students attending in-person lectures on campus seemed less likely to become infected (aOR: 0.34, 95% CI: 0.15-0.77). No association was found with other variables. The results of the second model were comparable to the first analysis. This study indicates that if universities adopt strict prevention measures, it is safe for students to attend, even in the case of an infectious disease epidemic.

Effectiveness of Enterovirus 71 inactivated vaccines against hand, foot, and mouth disease: A test-negative case-control study

ABSTRACT The Enterovirus A71 (EV-A71) vaccine was introduced in China in December 2015 as a preventive measure against hand, foot, and mouth disease (HFMD) caused by EV-A71. However, the effectiveness of the vaccine (VE) in real-world settings needs to be evaluated. We conducted a test-negative case-control study to assess the effectiveness of EV-A71 vaccines in preventing EV-A71-associated HFMD. Children aged 6–71 months with HFMD were enrolled as participants. The case group comprised those who tested positive for EV-A71, while the control group comprised those who tested negative for EV-A71. To estimate VE, a logistic regression model was employed, adjusting for potential confounders including age, gender, and clinical severity. In total, 3223 children aged 6 to 71 months were included in the study, with 162 in the case group and 3061 in the control group. The proportion of children who received EV-A71 vaccination was significantly lower in the case group compared to the control group (p < .001). The overall VEadj was estimated to be 90.8%. The VEadj estimates for partially and fully vaccinated children were 90.1% and 90.9%, respectively. Stratified by age group, the VEadj estimates were 88.7% for 6 to 35-month-olds and 95.5% for 36 to 71-month-olds. Regarding disease severity, the VEadj estimates were 86.3% for mild cases and 100% for severe cases. Sensitivity analysis showed minimal changes in the VE point estimates, with most changing by no more than 1% point. Our study demonstrates a high level of vaccine effectiveness against EV-A71-HFMD, especially in severe cases. Active promotion of EV-A71 vaccination is an effective strategy in preventing EV-A71 infections.

Risk factors for SARS-CoV-2 infection at a UK electricity-generating company: a test-negative design case-control study

ObjectivesIdentify workplace risk factors for SARS-CoV-2 infection, using data collected by a UK electricity-generating company.MethodsUsing a test-negative design case-control study, we estimated the OR of infection by job category, site,...

Factors associated with COVID-19 among hospitalized patients with severe acute respiratory infections in Serbia, 2022-2023: A test negative case-control study.

Severe acute respiratory infections (SARI) are estimated to be the cause of death in about 19% of all children younger than 5 years globally. The outbreak of coronaviral disease (COVID-19) caused by SARS-CoV-2, increased considerably the burden of SARI worldwide. We used data from a vaccine effectiveness study to identify the factors associated with SARS CoV-2 infection among hospitalized SARI patients. We recruited SARI patients at 3 hospitals in Serbia from 7 April 2022-1 May 2023. We collected demographic and clinical data from patients using a structured questionnaire, and all SARI patients were tested for SARS-CoV-2 by RT-PCR. We conducted an unmatched test negative case-control study. SARS-CoV-2 infected SARI patients were considered cases, while SARS CoV-2 negative SARI patients were controls. We conducted bivariate and multivariable logistic regression analysis in order to identify variables associated with SARS-CoV-2 infection. We included 110 SARI patients: 74 were cases and 36 controls. We identified 5 factors associated with SARS-CoV-2 positivity, age (OR = 1.04; 95% CI = 1.01-1.07), having received primary COVID-19 vaccine series (OR = 0.28; 95% CI = 0.09-0.88), current smoking (OR = 8.64; 95% CI = 2.43-30.72), previous SARS CoV-2 infection (OR = 3.48; 95% CI = 1.50-8.11) and number of days before seeking medical help (OR = 0.81; 95% CI = 0.64-1.02). In Serbia during a period of Omicron circulation, we found that older age, unvaccinated, hospitalized SARI patients, previously infected with SARS CoV-2 virus and those who smoked, were more likely to be SARS-CoV-2-positive; these patient populations should be prioritized for COVID vaccination.

Waning intra-season vaccine effectiveness against influenza A(H3N2) underlines the need for more durable protection

ABSTRACT Background The question of whether influenza vaccine effectiveness (VE) wanes over the winter season is still open and some contradictory findings have been reported. This study investigated the possible decline in protection provided by the available influenza vaccines. Research design and methods An individual-level pooled analysis of six test-negative case-control studies conducted in Italy between the 2018/2019 and 2022/2023 seasons was performed. Multivariable logistic regression analyses were performed to estimate weekly change in the odds of testing positive for influenza 14 days after vaccination. Results Of 6490 patients included, 1633 tested positive for influenza. Each week that had elapsed since vaccination was associated with an increase in the odds of testing positive for any influenza (4.9%; 95% CI: 2.0–8.0%) and for A(H3N2) (6.5%; 95% CI: 2.9–10.3%). This decline in VE was, however, significant only in children and older adults. A similar increase in the odds of testing positive was seen when the dataset was restricted to vaccinees only. Conversely, VE waning was less evident for A(H1N1)pdm09 or B strains. Conclusions Significant waning of VE, especially against influenza A(H3N2), may be one of the factors associated with suboptimal end-of-season VE. Next-generation vaccines should provide more durable protection against A(H3N2).

Waning effectiveness of mRNA COVID-19 vaccines against inpatient and emergency department encounters.

In the United States, most real-world estimates of COVID-19 vaccine effectiveness are based on data drawn from large health systems or sentinel populations. More data is needed to understand how the benefits of vaccination may vary across US populations with disparate risk profiles and policy contexts. We aimed to provide estimates of mRNA COVID-19 vaccine effectiveness against moderate and severe outcomes of COVID-19 based on state population-level data sources. Using statewide integrated administrative and clinical data and a test-negative case-control study design, we assessed mRNA COVID-19 vaccine effectiveness against SARS-CoV-2-related hospitalizations and emergency department visits among adults in South Carolina. We presented estimates of vaccine effectiveness at discrete time intervals for adults who received one, two or three doses of mRNA COVID-19 vaccine compared to adults who were unvaccinated. We also evaluated changes in vaccine effectiveness over time (waning) for the overall sample and in subgroups defined by age. We showed that while two doses of mRNA COVID-19 vaccine were initially highly effective, vaccine effectiveness waned as time elapsed since the second dose. Compared to protection against hospitalizations, protection against emergency department visits was found to wane more sharply. In all cases, a third dose of mRNA COVID-19 vaccine conferred significant gains in protection relative to waning protection after two doses. Further, over more than 120 days of follow-up, the data revealed relatively limited waning of vaccine effectiveness after a third dose of mRNA COVID-19 vaccine.

Interim Estimates of 2023-24 Seasonal Influenza Vaccine Effectiveness - United States.

In the United States, annual influenza vaccination is recommended for all persons aged ≥6 months. Using data from four vaccine effectiveness (VE) networks during the 2023-24 influenza season, interim influenza VE was estimated among patients aged ≥6 months with acute respiratory illness-associated medical encounters using a test-negative case-control study design. Among children and adolescents aged 6 months-17 years, VE against influenza-associated outpatient visits ranged from 59% to 67% and against influenza-associated hospitalization ranged from 52% to 61%. Among adults aged ≥18 years, VE against influenza-associated outpatient visits ranged from 33% to 49% and against hospitalization from 41% to 44%. VE against influenza A ranged from 46% to 59% for children and adolescents and from 27% to 46% for adults across settings. VE against influenza B ranged from 64% to 89% for pediatric patients in outpatient settings and from 60% to 78% for all adults across settings. These findings demonstrate that the 2023-24 seasonal influenza vaccine is effective at reducing the risk for medically attended influenza virus infection. CDC recommends that all persons aged ≥6 months who have not yet been vaccinated this season get vaccinated while influenza circulates locally.

Influenza vaccination during the 2021/22 season: A data-linkage test-negative case-control study of effectiveness against influenza requiring emergency care in England and serological analysis of primary care patients

We present England 2021/22 end-of-season adjusted vaccine effectiveness (aVE) against laboratory confirmed influenza related emergency care use in children aged 1–17 and in adults aged 50+, and serological findings in vaccinated vs unvaccinated adults by hemagglutination inhibition assay.Influenza vaccination has been routinely offered to all children aged 2–10 years and adults aged 65 years + in England. In 2021/22, the offer was extended to children to age 15 years, and adults aged 50–64 years. Influenza activity rose during the latter half of the 2021/22 season, while remaining comparatively low due to COVID-19 pandemic control measures. Influenza A(H3N2) strains predominated.A test negative design was used to estimate aVE by vaccine type. Cases and controls were identified within a sentinel laboratory surveillance system. Vaccine histories were obtained from the National Immunisation Management Service (NIMS), an influenza and COVID-19 vaccine registry. These were linked to emergency department presentations (excluding accidents) with respiratory swabbing ≤ 14 days before or ≤ 7 days after presentation. Amongst adults, 423 positive and 32,917 negative samples were eligible for inclusion, and 145 positive and 6,438 negative samples among children. Those admitted to hospital were further identified.In serology against the circulating A(H3N2) A/Bangladesh/4005/2020-like strain, 61 % of current season adult vaccinees had titres ≥ 1:40 compared to 17 % of those unvaccinated in 2020/21 or 2021/22 (p < 0.001).We found good protection from influenza vaccination against influenza requiring emergency care in children (72.7 % [95 % CI 52.7, 84.3 %]) and modest effectiveness in adults (26.1 % [95 % CI 4.5, 42.8 %]). Adult VE was higher for A(H1N1) (81 % [95 % CI 50, 93 %]) than A(H3N2) (33 % [95 % CI 6, 53 %]). Consistent protection was observable across preschool, primary and secondary school aged children. Imperfect test specificity combined with very low prevalence may have biased estimates towards null. With limited influenza circulation, the study could not determine differences by vaccine types.

Vaccine effectiveness against influenza hospitalisation in adults during the 2022/2023 mixed season of influenza A(H1N1)pdm09, A(H3N2) and B circulation, Europe: VEBIS SARI VE hospital network.

We conducted a multicentre hospital-based test-negative case-control study to measure vaccine effectiveness (VE) against PCR-confirmed influenza in adult patients with severe acute respiratory infection (SARI) during the 2022/2023 influenza season in Europe. Among 5547 SARI patients ≥18 years, 2963 (53%) were vaccinated against influenza. Overall VE against influenza A(H1N1)pdm09 was 11% (95% CI: -23-36); 20% (95% CI: -4-39) against A(H3N2) and 56% (95% CI: 22-75) against B. During the 2022/2023 season, while VE against hospitalisation with influenza B was >55%, it was ≤20% for influenza A subtypes. While influenza vaccination should be a priority for future seasons, improved vaccines against influenza are needed.

Effectiveness of the adapted bivalent mRNA COVID-19 vaccines against hospitalisation in individuals aged ≥ 60 years during the Omicron XBB lineage-predominant period: VEBIS SARI VE network, Europe, February to August, 2023.

We conducted a multicentre hospital-based test-negative case-control study to measure the effectiveness of adapted bivalent COVID-19 mRNA vaccines against PCR-confirmed SARS-CoV-2 infection during the Omicron XBB lineage-predominant period in patients aged ≥ 60 years with severe acute respiratory infection from five countries in Europe. Bivalent vaccines provided short-term additional protection compared with those vaccinated > 6 months before the campaign: from 80% (95% CI: 50 to 94) for 14-89 days post-vaccination, 15% (95% CI: -12 to 35) at 90-179 days, and lower to no effect thereafter.

Risk factors for SARS-CoV-2 infection: a test-negative case–control study with additional population controls in Norway

ObjectivesThis study aims to assess risk factors for SARS-CoV-2 infection by combined design; first comparing positive cases to negative controls as determined by PCR testing and then comparing these two...

Effectiveness of COVID-19 mRNA vaccine in preventing infection against Omicron strain: Findings from the Hiroshima Prefecture COVID-19 version J-SPEED for PCR center.

Despite the widespread adoption of various preventive measures since the spread of COVID-19, there remains a lack of consensus on universally acknowledged best practices. However, the significance of vaccination has risen to prominence as a paramount preventive strategy. Numerous investigations have demonstrated vaccine effectiveness against the omicron strain in severe disease and symptomatic disease, however, the scope of research pertaining to vaccine effectiveness in preventing infection is presently limited. Therefore, the current study aimed to evaluate COVID-19 mRNA (Pfizer-BioNTech BNT162b2 or Moderna mRNA-1273) vaccine effectiveness in preventing infection. We conducted a test-negative case-control study using a dataset of 117,335 individuals. These data were collected through the COVID-19 J-SPEED form in the PCR center at Hiroshima Prefecture, Japan from 1 February to 17 March 2022. We estimated propensity score matching for vaccine status based on participants' demographic characteristics. Subsequently, odds ratio was calculated from logistic regression to determine the association between vaccination status and test positivity rate adjusting for symptoms, exposure to close contact, and previous infection history. Vaccine effectiveness was defined as (1 -aORs) ×100%. The PCR test positivity rates were 7.9%, 4.5%, and 2.8% for the non-vaccinated (non-vaccinated, vaccinated with a single dose, and vaccinated with two doses less than 14 days ago), vaccinated with two doses (vaccinated over 14 days ago), and three doses, respectively. In unadjusted and adjusted analyses, vaccine effectiveness of two doses against infection were 38.5% (95% confidence interval [CI]: 32.8%-43.8%) and 34.7% (95%CI: 28.4%-40.4%), respectively, compared to non-vaccinated group. Vaccine effectiveness of three doses were 33.8% (95%CI: 25.0%-41.5%) and 26.4% (95%CI: 16.4%-35.2%), respectively, compared to those vaccinated with two doses. These results illustrate the protective effect of mRNA vaccines against Omicron strain infections and emphasize the significance of completing the suggested vaccination schedule.

Interim Estimates of 2023-2024 Seasonal Influenza Vaccine Effectiveness Among Adults in Korea.

In the 2023-2024 season, the influenza epidemic in South Korea peaked earlier than in recent years. In this study, we aimed to estimate the interim vaccine effectiveness (VE) of the influenza vaccination to prevent influenza during the early season. From November 1, 2023, to December 31, 2023, we enrolled 2,632 subjects with influenza-like illness from eight hospitals participating in hospital-based influenza morbidity and mortality surveillance. A retrospective test-negative case-control study was conducted to estimate the VE. The results showed an adjusted VE of 22.5% (95% confidence interval [CI], 6.6 to 35.8) for the total population. The adjusted VE was 22.3% (95% CI, 6.1 to 35.7) for influenza A and 9.4% (95% CI, -51.3 to 45.7) for influenza A/H1N1. Full results of the analysis will be reported.

Maternal Vaccine Effectiveness Against Influenza-Associated Hospitalizations and Emergency Department Visits in Infants

Influenza virus infection during pregnancy is associated with severe maternal disease and may be associated with adverse birth outcomes. Inactivated influenza vaccine during pregnancy is safe and effective and can protect young infants, but recent evidence, particularly after the 2009 novel influenza A (H1N1) pandemic, is limited. To evaluate the effectiveness of influenza vaccination during pregnancy against laboratory-confirmed influenza-associated hospitalizations and emergency department (ED) visits in infants younger than 6 months. This was a prospective, test-negative case-control study using data from the New Vaccine Surveillance Network from the 2016 to 2017 through 2019 to 2020 influenza seasons. Infants younger than 6 months with an ED visit or hospitalization for acute respiratory illness were included from 7 pediatric medical institutions in US cities. Control infants with an influenza-negative molecular test were included for comparison. Data were analyzed from June 2022 to September 2023. Maternal influenza vaccination during pregnancy. We estimated maternal vaccine effectiveness against hospitalizations or ED visits in infants younger than 6 months, those younger than 3 months, and by trimester of vaccination. Maternal vaccination status was determined using immunization information systems, medical records, or self-report. Vaccine effectiveness was estimated by comparing the odds of maternal influenza vaccination 14 days or more before delivery in infants with influenza vs those without. Of 3764 infants (223 with influenza and 3541 control infants), 2007 (53%) were born to mothers who were vaccinated during pregnancy. Overall vaccine effectiveness in infants was 34% (95% CI, 12 to 50), 39% (95% CI, 12 to 58) against influenza-associated hospitalizations, and 19% (95% CI, -24 to 48) against ED visits. Among infants younger than 3 months, effectiveness was 53% (95% CI, 30 to 68). Effectiveness was 52% (95% CI, 30 to 68) among infants with mothers who were vaccinated during the third trimester and 17% (95% CI, -15 to 40) among those with mothers who were vaccinated during the first or second trimesters. Maternal vaccination was associated with reduced odds of influenza-associated hospitalizations and ED visits in infants younger than 6 months. Effectiveness was greatest among infants younger than 3 months, for those born to mothers vaccinated during the third trimester, and against influenza-associated hospitalizations.

Inactivated vaccine effectiveness against symptomatic COVID-19 in Fujian, China during the Omicron BA.2 outbreak.

More than 90% of the Chinese population have completed 2 doses of inactivated COVID-19 vaccines in Mainland China. However, after China government abandoned strict control measures, many breakthrough infections appeared, and vaccine effectiveness against Omicron BA.2 infection was uncertain. This study aims to investigate the real-world effectiveness of widely used inactivated vaccines during the wave of Omicron variants. Test-negative case-control study was conducted in this study to analyze the vaccine effectiveness against symptomatic disease caused by the Omicron variant (BA.2) in Fujian, China. Conditional logistic regression was selected to estimate the vaccine effectiveness. The study found the vaccine effectiveness against symptomatic COVID-19 is 32.46% (95% CI, 8.08% to 50.37%) at 2 to 8 weeks, and 27.05% (95% CI, 1.23% to 46.12%) at 12 to 24 weeks after receiving booster doses of the inactivated vaccine. Notably, the 3-17 years group had higher vaccine effectiveness after 2 doses than the 18-64 years and over 65 years groups who received booster doses. Inactivated vaccines alone may not offer sufficient protection for all age groups before the summer of 2022. To enhance protection, other types of vaccines or bivalent vaccines should be considered.