Decline in seasonal influenza vaccine effectiveness with vaccination program maturation: A systematic review and meta-analysis

ObjectivesEvidence suggests repeated influenza vaccination may reduce vaccine effectiveness (VE). Using influenza vaccination program maturation (number of years since program inception) [PM] as proxy for population-level repeated vaccination, we assessed the impact on pooled adjusted end-season VE estimates from outpatient test-negative design studies.MethodsWe 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.ResultsWe included 72 articles from 11,931 unique citations. Across the three 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.ConclusionsThe evidence suggests 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

Seasonal influenza vaccination in older people: A systematic review and meta-analysis of the determining factors.

Background/objectivesDespite influenza vaccination programs in various jurisdictions, seasonal influenza vaccine (SIV) uptake remains suboptimal among older people (≥65years old), an important subpopulation for influenza vaccination. We sought to summarize determinants of SIV uptake (any vaccine receipt) and vaccination adherence (receipt of vaccine in two or more seasons in sequence) among older people.MethodsWe searched for population-based studies conducted in community-dwelling older people (irrespective of their health status) from 2000-2019. Two reviewers independently selected publications for inclusion. One reviewer extracted data from the included studies; a second checked the extracted data for errors. Disagreements were resolved by discussion and consensus, or a third reviewer. We were interested in the determinants of SIV uptake and vaccination adherence. Where appropriate, we pooled adjusted results using the inverse variance, random-effects method and reported the odds ratios (OR) and their 95% confidence intervals (CI).ResultsOut of 11,570 citations screened, we included 34 cross-sectional studies. The following were associated with increased SIV uptake: being older (OR 1.52, 95%CI 1.38-1.67 [21 studies]), white (1.30, 1.14-1.49 [10 studies]), married (1.23, 1.17-1.28 [9 studies]), non-smoker (1.28, 1.11-1.47 [7 studies]), of a higher social class (1.20, 1.06-1.36 [2 studies]), having a higher education (1.12, 1.04-1.21 [14 studies]), having a higher household income (1.11, 1.05-1.18 [8 studies]), having a chronic illness (1.53, 1.44-1.63 [16 studies]), having poor self-assessed health (1.23, 1.02-1.40 [9 studies]), having a family doctor (2.94, 1.79-4.76 [2 studies]), and having health insurance (1.58, 1.13-2.21 [6 studies]). The influence of these factors varied across geographical regions. Being older (1.26, 1.11-1.44 [2 studies]) was also associated with increased vaccination adherence.ConclusionsSeveral factors may determine SIV uptake and vaccination adherence among older people. More studies are needed to provide a stronger evidence base for planning more effective influenza vaccination programs