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Abstract Background The low influenza vaccine effectiveness (VE) observed during the A(H3N2)-dominated 2017–2018 season may be due to vaccine virus adaptation to growth in eggs. We compared the effectiveness of cell-cultured and egg-based vaccines among Medicare beneficiaries. Methods Retrospective cohort study on Medicare beneficiaries aged ≥65 years who received an influenza vaccine (cell-cultured, egg-based quadrivalent; egg-based high-dose, adjuvanted, or standard-dose trivalent) during the 2017–2018 season. We used Poisson regression to evaluate relative VE (RVE) in preventing influenza-related hospital encounters. Results Of >13 million beneficiaries, RVE for cell-cultured vaccines relative to egg-based quadrivalent vaccines was 10% (95% confidence interval [CI], 7%–13%). In a midseason interim analysis, this estimate was 16.5% (95% CI, 10.3%–22.2%). In a 5-way comparison, cell-cultured (RVE, 11%; 95% CI, 8%–14%) and egg-based high-dose (RVE, 9%; 95% CI, 7%–11%) vaccines were more effective than egg-based quadrivalent vaccines. Conclusions The modest VE difference between cell-cultured and egg-based vaccines only partially explains the low overall VE reported by the Centers for Disease Control and Prevention, suggesting that egg adaptation was not the main contributor to the low VE found among individuals aged ≥65 years. The midseason interim analysis we performed demonstrates that our methods can be used to evaluate VE actively during the influenza season. Among >13 million Medicare beneficiaries, the cell-cultured vaccine was more effective than the comparable egg-based vaccine during the 2017–2018 season. However, the marginal difference in effectiveness observed only partially explains the overall low vaccine effectiveness reported during the season.

•Vaccine effectiveness in children visiting an Emergency Department for influenza.•Test negative case-control study in 11 paediatric centres in two influenza seasons.•Vaccine effectiveness in preventing ED visits: 38% (95% CI −52% to 75%).•Add information for recommendation for vaccination in children. To evaluate the effectiveness of seasonal influenza vaccine in preventing Emergency Department (ED) visits and hospitalisations for influenza like illness (ILI) in children. We conducted a test negative case-control study during the 2011–2012 and 2012–2013 influenza seasons. Eleven paediatric hospital/wards in seven Italian regions participated in the study. Consecutive children visiting the ED with an ILI, as diagnosed by the doctor according to the European Centre for Disease Control case definition, were eligible for the study. Data were collected from trained pharmacists/physicians by interviewing parents during the ED visit (or hospital admission) of their children. An influenza microbiological test (RT-PCR) was carried out in all children. Seven-hundred and four children, from 6 months to 16 years of age, were enrolled: 262 children tested positive for one of the influenza viruses (cases) and 442 tested negative (controls). Cases were older than controls (median age 46 vs. 29 months), though with a similar prevalence of chronic conditions. Only 25 children (4%) were vaccinated in the study period. The overall age-adjusted vaccine effectiveness (VE) was 38% (95% confidence interval −52% to 75%). A higher VE was estimated for hospitalised children (53%; 95% confidence interval −45% to 85%). This study supports the effectiveness of the seasonal influenza vaccine in preventing visits to the EDs and hospitalisations for ILI in children, although the estimates were not statistically significant and with wide confidence intervals. Future systematic reviews of available data will provide more robust evidence for recommending influenza vaccination in children.

Introduction Measles is an extremely contagious viral disease that can be prevented through vaccination. It is caused by the measles virus and presents with symptoms such as high fever, cough, runny nose, conjunctivitis, and a distinctive rash. Complications may include pneumonia, diarrhoea, and neurological issues. The disease spreads through respiratory droplets and continues to pose a significant public health challenge, especially in Africa, despite vaccination efforts. Objective This systematic review and meta-analysis aim to estimate the pooled vaccine effectiveness of measles vaccines among African children, providing insights into immunization program success and informing policy decisions on vaccine distribution and resource allocation. Methods Following PRISMA guidelines, search was conducted in databases including PubMed/Medline, Science Direct, HINARI, Cochrane/Wiley library, Europe PMC, and grey literatures like Google Scholar up to March 2024. Cross-sectional studies assessed measles vaccine effectiveness in African children aged nine months and above were included. Data was extracted using JBI extraction tool and entered into microsoft excel and analysed via STATA version 20.1 using random effect model. Results From 5295 identified articles, 18 met the inclusion criteria, encompassing 26,470 children from 13 African countries. The pooled measles vaccine effectiveness was 68.58%, with significant heterogeneity (I2 = 99.66%, p  < 0.001). Subgroup analysis showed variability in vaccine effectiveness by study period, with higher effectiveness in studies conducted after the Global Vaccine Action Plan (GVAP) in 2012. Conclusion Measles vaccine effectiveness varies in African regions, ranging from 98.4% in Nigeria to 36.5% in Mozambique, with an overall effectiveness of 68.58% and high heterogeneity among studies. Optimizing vaccine distribution, increasing coverage, and prompt administration are important for enhancing effectiveness. Continued support for GVAP strategies and further research is needed to understand factors affecting vaccine performance and improve immunization efforts in Africa.

•Immunity after 5 doses of DTaP vaccine does not wane rapidly in young children.•Vaccine effectiveness against pertussis was ~90% in fully vaccinated children.•We used survival analysis methods to estimate time-varying vaccine effects. Waning of immunity after vaccination with the acellular Pertussis (aP) vaccine has been proposed as one of the main reasons for pertussis resurgence in the US. In this study, we estimated time-varying vaccine effectiveness after 5 doses of aP vaccine. We conducted a retrospective cohort study among children 5–9 years old (born between 2008 and 2012) living in King County, Washington, USA, who participated in the Washington State Immunization Information System. We estimated time-varying vaccine effectiveness after 5 doses of aP using smoothed scaled Schoenfeld residuals obtained from fitting Cox proportional hazards models to the data as well as piecewise constant Poisson regression. There were 55 pertussis cases in this cohort, of whom 22 (40%) were fully-vaccinated and 33 (60%) were under-vaccinated. Vaccine effectiveness (VE) remained high for up to 42 months after the fifth dose (VE(t) = 89%; 95% CI: 64%, 97%) as estimated using survival analysis methods and up to 4 years (VE(t) = 93%; 95% CI: 67%, 98%) as estimated using Poisson regression. We did not find evidence for waning of vaccine effectiveness for up to four years after 5 doses of aP among 5 –9 years old children in King County, WA.

The objective of this study was to estimate, by a novel spatiotemporal approach in an environment of non-funded rotavirus (RV) vaccines, the RV vaccine effectiveness (VE) to prevent acute gastroenteritis primary care (AGE-PC)–attended episodes, demonstrating how indirect protection leads to underestimation of direct VE under high vaccine coverage (VC). This population-based retrospective cohort study used electronic healthcare registries including all children 2 months–5 years old, born from 2009 to 2018 in the Valencia Region (Spain). Direct RV VE preventing AGE-PC episodes was estimated using propensity score matching and Poisson regressions stratified by VC, adjusted by age and calendar season. Indirect VE was estimated by Poisson regression comparing AGE-PC rates in unvaccinated children among the different VC levels. A total of 563,442 children were included for the RV VC estimation; of them, 360,576 were included in the birth-cohort for VE analysis. RV VC showed strong variability among districts and seasons, rising on average from 21% in 2009/2010 to 55% in 2017/2018. The highest direct VE was found in vaccinated children from districts with 0–30% RV VC (16.4%) and the lowest in those from districts with ≥ 70% RV VC (9.7%). The indirect protection in unvaccinated children raised from 6 to 16.6% for those living with 20–30% and ≥ 70% VC, respectively. Conclusion : Considering that RV is the causative agent in 20% of AGE cases, a direct effectiveness of 82% preventing AGE-PC episodes due to RV could be deduced using a novel spatiotemporal approach. A reduction of 17% of AGE-PC episodes in unvaccinated was observed in areas with VC over 70% because of indirect protection. What is Known: • The effectiveness of RV vaccines preventing hospitalizations due to RV-acute gastroenteritis (RV-AGE) has been extensively studied. However, RV also burdens the primary care (PC) setting, and data on vaccine effectiveness (VE) in preventing AGE-PC visits are scarce. • The RV vaccine distribution in Spain (non-funded), with large differences in vaccine coverage (VC) among healthcare districts, provides an ideal scenario to assess the actual VE in preventing AGE-PC consultations, including the direct and indirect protection . What is New: • A direct effectiveness of 82% preventing AGE-PC episodes due to RV could be deduced using a novel spatiotemporal approach. A reduction of 17% of AGE-PC episodes in unvaccinated was observed in areas with high VC because of indirect protection. • These findings, together with existing data on the impact on hospitalizations due to RV-AGE, offer valuable insights for implementing vaccination initiatives in countries that have not yet commenced such programs.

In April 2021, a COVID-19 outbreak occurred at a correctional facility in rural Virginia, USA. Eighty-four infections were identified among 854 incarcerated persons by facilitywide testing with reverse transcription quantitative PCR (qRT-PCR). We used whole-genome sequencing to link all infections to 2 employees infected with the B.1.1.7α (UK) variant. The relative risk comparing unvaccinated to fully vaccinated persons (mRNA-1273 [Moderna, https://www.modernatx.com]) was 7.8 (95% CI 4.8–12.7), corresponding to a vaccine effectiveness of 87.1% (95% CI 79.0%–92.1%). Average qRT-PCR cycle threshold values were lower, suggesting higher viral loads, among unvaccinated infected than vaccinated cases for the nucleocapsid, envelope, and spike genes. Vaccination was highly effective at preventing SARS-CoV-2 infection in this high-risk setting. This approach can be applied to similar settings to estimate vaccine effectiveness as variants emerge to guide public health strategies during the ongoing pandemic.

Benefit conferred by “enhanced” influenza vaccines is often measured by relative vaccine effectiveness, (rVE), which compares disease risk among groups of people who received alternative vaccines. Differences in attenuation of illness severity by vaccine types could manifest as differences in rVE. Using a simulated VE study and cohort of adults aged ≥ 65 years, we examined how rVE varied with assumptions about attenuation of disease severity conferred by standard and enhanced vaccines and how this variation could lead to differing estimates of rVE for prevention of moderate (i.e., outpatient) versus severe (i.e., inpatient) influenza illness. We found that if enhanced vaccines attenuated severe illness more than moderate illness, then rVE observed against severe disease could be higher than rVE observed against moderate disease. Thus, if differences in disease attenuation by vaccine type occurs, estimates of rVE may vary for influenza outcomes of differing levels of severity.

The real-world effectiveness of the coronavirus disease 2019 (COVID-19) vaccines in Japan remains unclear. This case–control study evaluated the vaccine effectiveness (VE) of two doses of mRNA vaccine, BNT162b2 or mRNA-1273, against the delta (B.1.617.2) variant in the Japanese general population in the period June–September 2021. Individuals in close contact with COVID-19 patients were tested using polymerase chain reaction (PCR). A self-administered questionnaire evaluated vaccination status, demographic data, underlying medical conditions, lifestyle, personal protective health behaviors, and living environment. Two vaccine doses were reported by 11.6% of cases (n = 389) and 35.2% of controls (n = 179). Compared with controls, cases were younger and had a lower proportion who always performed handwashing for ≥20 s, a higher proportion of alcohol consumers, and a lower proportion of individuals living in single-family homes or with commuting family members. After adjusting for these confounding factors and day of PCR testing by multivariate logistic regression analysis, the VE in the period June–July (delta variant proportion 45%) was 92% and 79% in the period August–September (delta variant proportion 89%). The adjusted VE for homestay, hotel-based isolation and quarantine, and hospitalization was 78%, 77%, and 97%, respectively. Despite declining slightly, VE against hospitalization remained robust for ~3 months after the second dose. Vaccination policymaking will require longer-term monitoring of VE against new variants.