scholarly journals Simple models to include influenza vaccination history when evaluating the effect of influenza vaccination

2021 ◽  
Vol 26 (32) ◽  
Author(s):  
Iván Martínez-Baz ◽  
Ana Navascués ◽  
Itziar Casado ◽  
Aitziber Aguinaga ◽  
Carmen Ezpeleta ◽  
...  
Keyword(s):  
Influenza Vaccination ◽  
Vaccine Effectiveness ◽  
Influenza B ◽  
Effect Modifier ◽  
Current Season ◽  
Percentage Points ◽  
Vaccination History ◽  
Modifying Effect ◽  
Effectiveness Studies ◽  
Influenza Vaccinations

Background Most reports of influenza vaccine effectiveness consider current-season vaccination only. Aim We evaluated a method to estimate the effect of influenza vaccinations (EIV) considering vaccination history. Methods We used a test-negative design with well-documented vaccination history to evaluate the average EIV over eight influenza seasons (2011/12–2018/19; n = 10,356). Modifying effect was considered as difference in effects of vaccination in current and previous seasons and current-season vaccination only. We also explored differences between current-season estimates excluding from the reference category people vaccinated in any of the five previous seasons and estimates without this exclusion or only for one or three previous seasons. Results The EIV was 50%, 45% and 38% in people vaccinated in the current season who had previously received none, one to two and three to five doses, respectively, and it was 30% and 43% for one to two and three to five prior doses only. Vaccination in at least three previous seasons reduced the effect of current-season vaccination by 12 percentage points overall, 31 among outpatients, 22 in 9–65 year-olds, and 23 against influenza B. Including people vaccinated in previous seasons only in the unvaccinated category underestimated EIV by 9 percentage points on average (31% vs 40%). Estimates considering vaccination of three or five previous seasons were similar. Conclusions Vaccine effectiveness studies should consider influenza vaccination in previous seasons, as it can retain effect and is often an effect modifier. Vaccination status in three categories (current season, previous seasons only, unvaccinated) reflects the whole EIV.

scholarly journals Influence of Prior Influenza Vaccination on Current Influenza Vaccine Effectiveness in Children Aged 1 to 5 Years

Vaccines ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 1447
Author(s):  
Kazuhiro Matsumoto ◽  
Wakaba Fukushima ◽  
Saeko Morikawa ◽  
Masashi Fujioka ◽  
Tohru Matsushita ◽  
...  
Keyword(s):  
Influenza Vaccination ◽  
Reference Group ◽  
Vaccination Strategy ◽  
Negative Influence ◽  
Vaccine Effectiveness ◽  
Vaccination Status ◽  
Current Season ◽  
Vaccination Rates ◽  
Vaccination History ◽  
Group 2

Background: Although annual influenza vaccination is an important strategy used to prevent influenza-related morbidity and mortality, some studies have reported the negative influence of prior vaccination on vaccine effectiveness (VE) for current seasons. Currently, the influence of prior vaccination is not conclusive, especially in children. Methods: We evaluated the association between current-season VE and prior season vaccination using a test-negative design in children aged 1–5 years presenting at nine outpatient clinics in Japan during the 2016/17 and 2017/18 influenza seasons. Children with influenza-like illness were enrolled prospectively and tested for influenza using real-time RT-PCR. Their recent vaccination history was categorized into six groups according to current vaccination doses (0/1/2) and prior vaccination status (unvaccinated = 0 doses/vaccinated = 1 dose or 2 doses): (1) 0 doses in the current season and unvaccinated in prior seasons (reference group); (2) 0 doses in the current season and vaccinated in a prior season; (3) 1 dose in the current season and unvaccinated in a prior season; (4) 1 dose in the current season and vaccinated in a prior season; (5) 2 doses in the current season and unvaccinated in a prior season, and (6) 2 doses in the current season and vaccinated in a prior season. Results: A total of 799 cases and 1196 controls were analyzed. The median age of the subjects was 3 years, and the proportion of males was 54%. Overall, the vaccination rates (any vaccination in the current season) in the cases and controls were 36% and 53%, respectively. The VEs of the groups were: (2) 29% (95% confidence interval: −25% to 59%); (3) 53% (6% to 76%); (4) 70% (45% to 83%); (5) 56% (32% to 72%), and (6) 61% (42% to 73%). The one- and two-dose VEs of the current season were significant regardless of prior vaccination status. The results did not differ when stratified by influenza subtype/lineage. Conclusion: Prior vaccination did not attenuate the current-season VE in children aged 1 to 5 years, supporting the annual vaccination strategy.

scholarly journals Vaccine effectiveness against influenza-associated hospitalization among children aged < 13 years using a hospital-based surveillance system in Minnesota, 2013 – 2016

2017 ◽  
Vol 4 (suppl_1) ◽  
pp. S60-S60
Author(s):  
Ashley Fowlkes ◽  
Hannah Friedlander ◽  
Andrea Steffens ◽  
Kathryn Como-Sabetti ◽  
Dave Boxrud ◽  
...  
Keyword(s):  
Influenza Vaccine ◽  
Influenza Vaccination ◽  
Influenza A ◽  
Respiratory Illness ◽  
Vaccine Effectiveness ◽  
Influenza Viruses ◽  
Point Estimate ◽  
Influenza B ◽  
Current Season ◽  
Immunization Registry

Abstract Background Due to marked variability in circulating influenza viruses each year, annual evaluation of the vaccine’s effectiveness against severe outcomes is essential. We used the Minnesota Department of Health’s (MDH) Severe Acute Respiratory Illness (SARI) surveillance to evaluate vaccine effectiveness (VE) against influenza-associated hospitalization over three influenza seasons. Methods Residual respiratory specimens from patients admitted with SARI were sent to the MDH laboratory for influenza RT-PCR testing. Medical records were reviewed to collect patient data. Vaccination history was verified using the state immunization registry. We included patients aged ≥6 months to &lt; 13 years, after which immunization reporting is not required, hospitalized from the earliest influenza detection after July through April each year. We defined vaccinated patients as those ≥1 dose of influenza vaccine in the current season. Children aged &lt; 9 years with no history of vaccination were considered vaccinated if 2 were doses given a month apart. Partially vaccinated children were excluded. We estimated VE as 1 minus the adjusted odds ratio (x100%) of influenza vaccination among influenza cases vs. negative controls, controlling for age, race, days from onset to admission, comorbidities, and admission month. Results Among 2198 SARI patients, 763 (35%) were vaccinated for influenza, 180 (8.2%) were partially vaccinated, and 1255 (57%) were unvaccinated. Influenza was detected among 202 (9.2%) children, and significantly more frequently among children aged ≥5 years (17%) compared with younger children (7.4%). The adjusted VE in 2013–14 was 68% (95% Confidence Interval: 34, 85), but was non-significant during the 2014–15 and 2015–16 seasons (Figure). Estimates of VE by influenza A subtypes varied substantially by year; VE against influenza B viruses was significant, but could not be stratified by year. VE was impacted when live attenuated influenza vaccine recipients were excluded. Conclusion We report moderately high influenza VE in 2013–14 and a point estimate higher than other published estimates from outpatient data in 2014–15. These results, underscore the importance of influenza vaccination to prevent severe outcomes such as hospitalization. Disclosures All authors: No reported disclosures.

scholarly journals Influenza vaccine effectiveness against hospitalization in the United States, 2019-2020

2020 ◽  
Author(s):  
Mark W Tenforde ◽  
H Keipp Talbot ◽  
Christopher H Trabue ◽  
Manjusha Gaglani ◽  
Tresa M McNeal ◽  
...  
Keyword(s):  
United States ◽  
Influenza Vaccine ◽  
Influenza Vaccination ◽  
Respiratory Illness ◽  
The United States ◽  
Vaccine Effectiveness ◽  
Influenza Viruses ◽  
Current Season ◽  
Hospital Resources ◽  
Negative Controls

Abstract Background Influenza causes significant morbidity and mortality and stresses hospital resources during periods of increased circulation. We evaluated the effectiveness of the 2019-2020 influenza vaccine against influenza-associated hospitalizations in the United States. Methods We included adults hospitalized with acute respiratory illness at 14 hospitals and tested for influenza viruses by reserve transcription polymerase chain reaction. Vaccine effectiveness (VE) was estimated by comparing the odds of current-season influenza vaccination in test-positive influenza cases versus test-negative controls, adjusting for confounders. VE was stratified by age and major circulating influenza types along with A(H1N1)pdm09 genetic subgroups. Results 3116 participants were included, including 18% (553) influenza-positive cases. Median age was 63 years. Sixty-seven percent (2079) received vaccination. Overall adjusted VE against influenza viruses was 41% (95% confidence interval [CI]: 27-52). VE against A(H1N1)pdm09 viruses was 40% (95% CI: 24-53) and 33% against B viruses (95% CI: 0-56). Of the two major A(H1N1)pdm09 subgroups (representing 90% of sequenced H1N1 viruses), VE against one group (5A+187A,189E) was 59% (95% CI: 34-75) whereas no significant VE was observed against the other group (5A+156K) [-1%, 95% CI: -61-37]. Conclusions In a primarily older population, influenza vaccination was associated with a 41% reduction in risk of hospitalized influenza illness.

scholarly journals Influenza vaccine effectiveness against laboratory-confirmed influenza in hospitalised adults aged 60 years or older, Valencia Region, Spain, 2017/18 influenza season

2019 ◽  
Vol 24 (31) ◽  
Author(s):  
Ainara Mira-Iglesias ◽  
F Xavier López-Labrador ◽  
Víctor Baselga-Moreno ◽  
Miguel Tortajada-Girbés ◽  
Juan Mollar-Maseres ◽  
...  
Keyword(s):  
Influenza Vaccine ◽  
Influenza A ◽  
Vaccine Effectiveness ◽  
Influenza Viruses ◽  
Influenza B ◽  
Current Season ◽  
Hospitalised Patients ◽  
Influenza A H1n1 ◽  
Vaccine Type ◽  
The Impact

Introduction Influenza immunisation is recommended for elderly people each season. The influenza vaccine effectiveness (IVE) varies annually due to influenza viruses evolving and the vaccine composition. Aim To estimate, in inpatients ≥ 60 years old, the 2017/18 trivalent IVE, overall, by vaccine type and by strain. The impact of vaccination in any of the two previous seasons (2016/17 and 2015/16) on current (2017/18) IVE was also explored. Methods This was a multicentre prospective observational study within the Valencia Hospital Surveillance Network for the Study of Influenza and Respiratory Viruses Disease (VAHNSI, Spain). The test-negative design was applied taking laboratory-confirmed influenza as outcome and vaccination status as main exposure. Information about potential confounders was obtained from clinical registries and/or by interviewing patients; vaccine information was only ascertained by registries. Results Overall, 2017/18 IVE was 9.9% (95% CI: −15.5 to 29.6%), and specifically, 48.3% (95% CI: 13.5% to 69.1%), −29.9% (95% CI: −79.1% to 5.8%) and 25.7% (95% CI: −8.8% to 49.3%) against A(H1N1)pdm09, A(H3N2) and B/Yamagata lineage, respectively. For the adjuvanted and non-adjuvanted vaccines, overall IVE was 10.0% (95% CI: −24.4% to 34.9%) and 7.8% (95% CI: −23.1% to 31.0%) respectively. Prior vaccination significantly protected against influenza B/Yamagata lineage (IVE: 50.2%; 95% CI: 2.3% to 74.6%) in patients not vaccinated in the current season. For those repeatedly vaccinated against influenza A(H1N1)pdm09, IVE was 46.4% (95% CI: 6.8% to 69.2%). Conclusion Our data revealed low vaccine effectiveness against influenza in hospitalised patients ≥60 years old in 2017/18. Prior vaccination protected against influenza A(H1N1)pdm09 and B/Yamagata-lineage.

scholarly journals 2553. Individual Patient-Level Data Meta-Analysis of Live Attenuated and Inactivated Influenza Vaccine Effectiveness Among US Children, 2013–2014 Through 2015–2016

2018 ◽  
Vol 5 (suppl_1) ◽  
pp. S68-S68
Author(s):  
Jessie Chung ◽  
Brendan Flannery ◽  
Rodolfo Begue ◽  
Herve Caspard ◽  
Laurie Demarcus ◽  
...  
Keyword(s):  
Influenza Vaccine ◽  
Influenza A ◽  
The United States ◽  
Vaccine Effectiveness ◽  
Vaccination Status ◽  
Influenza B ◽  
Rt Pcr ◽  
Current Season ◽  
Influenza A H1n1 ◽  
Vaccine Type

Abstract Background Quadrivalent live attenuated influenza vaccine (LAIV4) was not recommended for use in the United States for the 2016–2017 and 2017–2018 influenza seasons based on US observational studies of vaccine effectiveness (VE) from 2013–2014 to 2015–2016. We pooled individual patient data on children aged 2–17 years enrolled in 5 US studies during these 3 influenza seasons to further investigate VE by vaccine type. Methods Analyses included 17,173 children enrolled in the US Department of Defense Global Laboratory-based Influenza Surveillance Program, US Influenza Vaccine Effectiveness Network, Influenza Incidence Surveillance Project, Influenza Clinical Investigation for Children, and a Louisiana State University study. Participants’ specimens were tested for influenza by reverse transcription-polymerase chain reaction (RT-PCR), culture, or a combination of rapid antigen testing and RT-PCR. VE was calculated by comparing odds of vaccination with either inactivated influenza vaccine (IIV) or LAIV4 among influenza-positive cases to test-negative controls and calculated as 100 × (1 − odds ratio) in logistic regression models with age, calendar time, influenza season, and study site (random effect). Patients were stratified by prior season vaccination status in a subanalysis. Results Overall, 38% of patients (N = 6,558) were vaccinated in the current season, of whom 30% (N = 1,979) received LAIV4. Pooled VE of IIV against any influenza virus was 51% (95% CI: 47, 54) versus 26% (95% CI: 15, 36) for LAIV4. Point estimates for pooled VE against any influenza by age group ranged from 45% to 58% for IIV and 19% to 34% for LAIV4 during the 3 seasons (Figures 1 and 2). Pooled VE against influenza A(H1N1)pdm09 was 67% (95% CI: 62, 72) for IIV versus 20% (95% CI: −6, 39) for LAIV4. Pooled VE against influenza A(H3N2) was 29% (95% CI: 14, 42) for IIV versus 7% (95% CI: −11, 23) for LAIV4, and VE against influenza B was 52% (95% CI: 42, 60) for IIV and 66% (95% CI: 47, 77) for LAIV4. VE against influenza A(H1N1)pdm09 was lower for LAIV4 versus IIV across all strata of prior season vaccination (Figure 3). Conclusion Consistent with individual studies, our pooled analyses found that LAIV4 effectiveness was reduced for all age groups against influenza A(H1N1)pdm09 compared with IIV. This result did not vary based on prior vaccination status. Disclosures H. Caspard, AstraZeneca: Employee, Salary.

Classification of excluded or missing virology data from UK-wide influenza vaccine effectiveness studies (Preprint)

2018 ◽  
Author(s):  
Rebecca Webb ◽  
Mariya Hriskova ◽  
Ivelina Yonova ◽  
Manasa Tripathy ◽  
Sam Peters ◽  
...  
Keyword(s):  
Vaccine Effectiveness ◽  
Data Loss ◽  
Sentinel Network ◽  
Vaccination History ◽  
Using Data ◽  
The Uk ◽  
Impact Data ◽  
Effectiveness Studies ◽  
Identifiable Data

BACKGROUND Monitoring the effectiveness of the influenza vaccination programme within the UK is necessary in order to assess its clinical impact. Data are collected from general practice sentinel network computerised medical record (CMR) systems on patients from whom virology specimens have been taken for influenza. The data collected includes demographics, comorbidities, vaccine exposure and if patients have had a virology specimen taken. Unfortunately not all virology specimens collected can be used in the vaccine effectiveness (VE) studies conducted. OBJECTIVE To describe the proportion, reasons and any trends in virology specimen data collected but not used in influenza VE analyses, with the goal of defining strategies to reduce collection of specimens ineligible for use in VE studies. METHODS We examined UK influenza VE studies from the past 10 years and identified incidences where data were labelled unusable. We categorised reasons for not using data as: (1) Vaccination history: Missing or Uncertain categories (including patient not registered with the practice at the start of the season); (2) Swab timing: Not recorded; More than 7 days (historically over 29 days) after symptom onset or within 14 days of vaccination; (3) Laboratory: Not sufficient data for processing (e.g. no age), CT values; (4) Flu or vaccination type of no interest (including pandemic years). The proportion, reasons and trends for data loss were identified through descriptive statistics and graphical representations. We included an analysis of where other data had been available at the point of analysis but not used. RESULTS Over 30% (13292/41337) of virology specimen data was not used across all seasons. Data loss gradually began to decrease from 2014/15 onwards. Data loss were highest for flu or vaccination type of no interest and swab timing. Retrospective and prospective actions were identified to reduce data loss in future. Around 60% of samples could have been included if identifiable data were better shared between records. CONCLUSIONS The reasons for excluding samples and missing data varied, particularly prior to 2014; consistent categorisation was in place from 2014 onwards. Leaving aside the different issues around pandemic years, many of the virology swabs not included were due to suboptimal case selection by practices, but over half (58%) could have been included if identifiable data were better shared between data sources. CLINICALTRIAL N/A

scholarly journals 2760. Accounting for Vaccination History in Estimates of Current Season Vaccine Effectiveness in the US Flu VE Network, 2012–2013 Through 2017–2018

2019 ◽  
Vol 6 (Supplement_2) ◽  
pp. S973-S973
Author(s):  
Sara S Kim ◽  
Ivo Foppa ◽  
Jessie R Chung ◽  
Edward Belongia ◽  
Huong McLean ◽  
...  
Keyword(s):  
Respiratory Illness ◽  
Vaccine Effectiveness ◽  
Rt Pcr ◽  
Time High Risk ◽  
Calendar Time ◽  
Current Season ◽  
The Us ◽  
Vaccination History ◽  
Referent Group ◽  
Network Studies

Abstract Background Current season vaccine effectiveness (VE) and influenza risk may vary in persons based on vaccination history. United States Influenza Vaccine Effectiveness (US Flu VE) Network studies have explored prior vaccination effects using a single referent group of patients unvaccinated in both the prior and current seasons. We investigated vaccine benefit among those with and without prior season vaccination. Methods Our analysis included data from the US Flu VE Network among patients aged ≥9 years old with acute respiratory illness during 6 influenza seasons, 2012–2013 through 2017–2018. We determined current and prior season vaccination status from documented immunizations. Current season VE against laboratory confirmed influenza was estimated using multivariate logistic regression with an interaction term for prior and current season vaccination. Models were adjusted for age, calendar time, high-risk status, and site. Results Of 31,819 patients included in the analysis over 6 seasons, 9188 were influenza positive by RT–PCR. Percent flu positivity was greatest among those unvaccinated (34%), followed by those vaccinated in the prior season only (29%), those vaccinated in both seasons (25%), and those vaccinated in the current season only (23%). Among patients with prior season vaccination, current season VE against any influenza was 14% (95% CL: 5, 22) and against A(H3N2), A(H1N1)pdm09, and B was 10% (95% CL: 3, 17), 36% (95%CL: 25, 46), and 40% (95% CL: 33, 46), respectively. Among patients unvaccinated in the prior season, VE was 42% (95% CL: 37, 46) against any influenza in the current season and was 31% (95%CL: 22, 39), 57% (95% CL: 47, 65), and 55% (95% CL: 48, 61) against A(H3N2), A(H1N1)pdm09, and B, respectively. We observed significant interaction of prior season vaccination on current season VE in 4 of 6 seasons (P < 0.20). Conclusion Current season vaccination was overall protective regardless of vaccination history. Among those vaccinated in the prior season, current season vaccination may provide some benefit in addition to residual protection from previous vaccination. Disclosures All authors: No reported disclosures.

scholarly journals Effects of Prior Season Vaccination on Current Season Vaccine Effectiveness in the United States Flu Vaccine Effectiveness Network, 2012–2013 Through 2017–2018

2020 ◽  
Author(s):  
Sara S Kim ◽  
Brendan Flannery ◽  
Ivo M Foppa ◽  
Jessie R Chung ◽  
Mary Patricia Nowalk ◽  
...  
Keyword(s):  
Respiratory Illness ◽  
The United States ◽  
Vaccine Effectiveness ◽  
Influenza B ◽  
Time High Risk ◽  
Calendar Time ◽  
Vaccine Protection ◽  
Current Season ◽  
The Us ◽  
Flu Vaccine

Abstract Background We compared effects of prior vaccination and added or lost protection from current season vaccination among those previously vaccinated. Methods Our analysis included data from the US Flu Vaccine Effectiveness Network among participants ≥9 years old with acute respiratory illness from 2012–2013 through 2017–2018. Vaccine protection was estimated using multivariate logistic regression with an interaction term for effect of prior season vaccination on current season vaccine effectiveness. Models were adjusted for age, calendar time, high-risk status, site, and season for combined estimates. We estimated protection by combinations of current and prior vaccination compared to unvaccinated in both seasons or current vaccination among prior vaccinated. Results A total of 31 819 participants were included. Vaccine protection against any influenza averaged 42% (95% confidence interval [CI], 38%–47%) among those vaccinated only the current season, 37% (95% CI, 33–40) among those vaccinated both seasons, and 26% (95% CI, 18%–32%) among those vaccinated only the prior season, compared with participants vaccinated neither season. Current season vaccination reduced the odds of any influenza among patients unvaccinated the prior season by 42% (95% CI, 37%–46%), including 57%, 27%, and 55% against A(H1N1), A(H3N2), and influenza B, respectively. Among participants vaccinated the prior season, current season vaccination further reduced the odds of any influenza by 15% (95% CI, 7%–23%), including 29% against A(H1N1) and 26% against B viruses, but not against A(H3N2). Conclusions Our findings support Advisory Committee on Immunization Practices recommendations for annual influenza vaccination. Benefits of current season vaccination varied among participants with and without prior season vaccination, by virus type/subtype and season.

The Impact of Prior Season Vaccination on Subsequent Influenza Vaccine Effectiveness to Prevent Influenza-related Hospitalizations Over 4 Influenza Seasons in Canada

2018 ◽  
Vol 69 (6) ◽  
pp. 970-979 ◽  
Author(s):  
M K Nichols ◽  
M K Andrew ◽  
L Ye ◽  
T F Hatchette ◽  
A Ambrose ◽  
...  
Keyword(s):  
Influenza Vaccine ◽  
Negative Impact ◽  
Conditional Logistic Regression ◽  
Vaccine Effectiveness ◽  
Influenza B ◽  
Current Season ◽  
Vaccination Recommendations ◽  
Vaccine Impact ◽  
H3n2 Influenza ◽  
The Impact

Abstract Background Recent studies have demonstrated the possibility of negative associations between prior influenza vaccines and subsequent influenza vaccine effectiveness (VE), depending on season and strain. We investigated this association over 4 consecutive influenza seasons (2011–2012 through 2014–2015) in Canada. Methods Using a matched test-negative design, laboratory-confirmed influenza cases and matched test-negative controls admitted to hospitals were enrolled. Patients were stratified into 4 groups according to influenza vaccine history (not vaccinated current and prior season [referent], vaccinated prior season only, vaccinated current season only, and vaccinated both current and prior season). Conditional logistic regression was used to estimate VE; prior vaccine impact was assessed each season for overall effect and effect stratified by age (<65 years, ≥65 years) and type/subtype (A/H1N1, A/H3N2, influenza B). Results Overall, mainly nonsignificant associations were observed. Trends of nonsignificant decreased VE among patients repeatedly vaccinated in both prior and current season relative to the current season only were observed in the A/H3N2-dominant seasons of 2012–2013 and 2014–2015. Conversely, in 2011–2012, during which B viruses circulated, and in 2013–2014, when A/H1N1 circulated, being vaccinated in both seasons tended to result in a high VE in the current season against the dominant circulating subtype. Conclusions Prior vaccine impact on subsequent VE among Canadian inpatients was mainly nonsignificant. Even in circumstances where we observed a trend of negative impact, being repeatedly vaccinated was still more effective than not receiving the current season’s vaccine. These findings favor continuation of annual influenza vaccination recommendations, particularly in older adults. Clinical Trials Registration NCT01517191.

scholarly journals Decline in Seasonal Influenza Vaccine Effectiveness With Vaccination Program Maturation: A Systematic Review and Meta-analysis

2021 ◽  
Vol 8 (3) ◽  
Author(s):  
George N Okoli ◽  
Florentin Racovitan ◽  
Tiba Abdulwahid ◽  
Syed K Hyder ◽  
Louise Lansbury ◽  
...  
Keyword(s):  
Influenza Vaccination ◽  
Meta Analysis ◽  
Population Level ◽  
Vaccine Effectiveness ◽  
Vaccination Program ◽  
Influenza B ◽  
Inverse Variance ◽  
Potential Impact ◽  
The Difference ◽  
The Impact

Abstract Background Evidence suggests that repeated influenza vaccination may reduce vaccine effectiveness (VE). Using influenza vaccination program maturation (PM; number of years since program inception) as a proxy for population-level repeated vaccination, we assessed the impact on pooled adjusted end-season VE estimates from outpatient test-negative design studies. Methods We systematically searched and selected full-text publications from January 2011 to February 2020 (PROSPERO: CRD42017064595). We obtained influenza vaccination program inception year for each country and calculated PM as the difference between the year of deployment and year of program inception. We categorized PM into halves (cut at the median), tertiles, and quartiles and calculated pooled VE using an inverse-variance random-effects model. The primary outcome was pooled VE against all influenza. Results We included 72 articles from 11 931 citations. Across the 3 categorizations of PM, a lower pooled VE against all influenza for all patients was observed with PM. Substantially higher reductions were observed in older adults (≥65 years). We observed similar results for A(H1N1)pdm09, A(H3N2), and influenza B. Conclusions The evidence suggests that influenza VE declines with vaccination PM. This study forms the basis for further discussions and examinations of the potential impact of vaccination PM on seasonal VE.

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