I-MOVE Multi-Centre Case Control Study 2010-11: Overall and Stratified Estimates of Influenza Vaccine Effectiveness in Europe

Abstract

BackgroundIn the third season of I-MOVE (Influenza Monitoring Vaccine Effectiveness in Europe), we undertook a multicentre case-control study based on sentinel practitioner surveillance networks in eight European Union (EU) member states to estimate 2010/11 influenza vaccine effectiveness (VE) against medically-attended influenza-like illness (ILI) laboratory-confirmed as influenza.MethodsUsing systematic sampling, practitioners swabbed ILI/ARI patients within seven days of symptom onset. We compared influenza-positive to influenza laboratory-negative patients among those meeting the EU ILI case definition. A valid vaccination corresponded to > 14 days between receiving a dose of vaccine and symptom onset. We used multiple imputation with chained equations to estimate missing values. Using logistic regression with study as fixed effect we calculated influenza VE adjusting for potential confounders. We estimated influenza VE overall, by influenza type, age group and among the target group for vaccination.ResultsWe included 2019 cases and 2391 controls in the analysis. Adjusted VE was 52% (95% CI 30-67) overall (N = 4410), 55% (95% CI 29-72) against A(H1N1) and 50% (95% CI 14-71) against influenza B. Adjusted VE against all influenza subtypes was 66% (95% CI 15-86), 41% (95% CI -3-66) and 60% (95% CI 17-81) among those aged 0-14, 15-59 and ≥60 respectively. Among target groups for vaccination (N = 1004), VE was 56% (95% CI 34-71) overall, 59% (95% CI 32-75) against A(H1N1) and 63% (95% CI 31-81) against influenza B.ConclusionsResults suggest moderate protection from 2010-11 trivalent influenza vaccines against medically-attended ILI laboratory-confirmed as influenza across Europe. Adjusted and stratified influenza VE estimates are possible with the large sample size of this multi-centre case-control. I-MOVE shows how a network can provide precise summary VE measures across Europe.

Interim estimates of 2013/14 vaccine effectiveness against influenza A(H1N1)pdm09 from Canada’s sentinel surveillance network, January 2014

“…Generalisability to regions with a different profile of vaccine uptake may be limited on that basis. In recent analyses, we [12] and others [29,30,42] have noted a trend toward improved VE with recurrent receipt of the A(H1N1)pdm09 antigen, although other studies have reported contrary findings [28,31,35]. Assessment of these effects may benefit from the additional power available in end-of-season analysis.…”

“…The 2013/14 mid-season VE estimate against influenza A(H1N1)pdm09 of ca 75% is in the upper range of recent seasons' VE estimates for nonadjuvanted TIV against A(H1N1)pdm09 reported since 2010 from Canada [11,12,21], Europe [28][29][30][31][32] and the US [33][34][35], which span ca 60-80%. With several times more influenza A(H1N1)pdm09 cases already contributing thus far in 2013/14 than in previous seasons in Canada, we are likely to converge upon a more stable and accurate estimate of TIV protection against A(H1N1) pdm09 infection this season.…”

2012/13 influenza vaccine effectiveness against hospitalised influenza A(H1N1)pdm09, A(H3N2) and B: estimates from a European network of hospitals

“…[5] The most recent estimates for TIV efficacy among non-institutionalized elderly are from a large European study, which found a 60% efficacy in those >60 years of age. [218] Limited data from tropical settings have comparable findings: a RCT conducted in Thailand of adults ≥ 60 years living in the community detected a relative risk reduction of ILI of 56% (decreased incidence from 11% to 5% during the study period). [219] Among institutionalized elderly, observational study on estimates of influenza VE in preventing medically-attended acute illness were slightly lower than the Cochrane review estimate, ranging from 20%-40%.…”

Observational studies and the difficult quest for causality: lessons from vaccine effectiveness and impact studies

“…The "cases" and "test-negative controls" both sought care for an influenza-like illness, typically defined as fever plus respiratory symptoms (17,26,(29)(30)(31), and the test-negative controls are those who test negative on the real-time reverse-transcriptase polymerase chain reaction (rRT-PCR) test for influenza virus.…”