2015/16 I‐MOVE/I‐MOVE+ multicentre case‐control study in Europe: Moderate vaccine effectiveness estimates against influenza A(H1N1)pdm09 and low estimates against lineage‐mismatched influenza B among children

Abstract

BackgroundDuring the 2015/16 influenza season in Europe, the cocirculating influenza viruses were A(H1N1)pdm09 and B/Victoria, which was antigenically distinct from the B/Yamagata component in the trivalent influenza vaccine.MethodsWe used the test‐negative design in a multicentre case‐control study in twelve European countries to measure 2015/16 influenza vaccine effectiveness (VE) against medically attended influenza‐like illness (ILI) laboratory‐confirmed as influenza. General practitioners swabbed a systematic sample of consulting ILI patients and a random sample of influenza‐positive swabs was sequenced. We calculated adjusted VE against influenza A(H1N1)pdm09, A(H1N1)pdm09 genetic group 6B.1 and influenza B overall and by age group.ResultsWe included 11 430 ILI patients, of which 2272 were influenza A(H1N1)pdm09 and 2901 were influenza B cases. Overall VE against influenza A(H1N1)pdm09 was 32.9% (95% CI: 15.5‐46.7). Among those aged 0‐14, 15‐64 and ≥65 years, VE against A(H1N1)pdm09 was 31.9% (95% CI: −32.3 to 65.0), 41.4% (95% CI: 20.5‐56.7) and 13.2% (95% CI: −38.0 to 45.3), respectively. Overall VE against influenza A(H1N1)pdm09 genetic group 6B.1 was 32.8% (95% CI: −4.1 to 56.7). Among those aged 0‐14, 15‐64 and ≥65 years, VE against influenza B was −47.6% (95% CI: −124.9 to 3.1), 27.3% (95% CI: −4.6 to 49.4) and 9.3% (95% CI: −44.1 to 42.9), respectively.ConclusionsVaccine effectiveness (VE) against influenza A(H1N1)pdm09 and its genetic group 6B.1 was moderate in children and adults, and low among individuals ≥65 years. Vaccine effectiveness (VE) against influenza B was low and heterogeneous among age groups. More information on effects of previous vaccination and previous infection is needed to understand the VE results against influenza B in the context of a mismatched vaccine.

Interim 2017/18 influenza seasonal vaccine effectiveness: combined results from five European studies

“…The good VE against medically attended influenza A(H1N1)pdm09 is consistent with historical data [ 12 ]. However, during the last influenza A(H1N1)pdm09 season in Europe (2015/16), the EU-PC VE of 33% against influenza A(H1N1)pdm09 in all age groups was lower than what we report here [ 13 ]. In the 2015/16 season, the influenza vaccine strain A/California/7/2009 (H1N1)pdm09 differed from the circulating strains which mainly belonged to the genetic subgroup 6B.1 (represented by A/Michigan/45/2015 (H1N1)pdm09).…”

“…However, it is difficult to compare these estimates against any influenza since the relative proportion of circulating (sub)types was different in the UK, where there was a higher proportion of circulating influenza A(H3N2) viruses, compared with most countries participating in the EU-PC study. In past seasons where circulating and vaccine lineages were different, contradictory results were observed [ 13 , 23 , 24 ]. Partial, but not full cross-protection between mismatched influenza B lineages has been suggested by two systematic reviews [ 25 , 26 ].…”

Determinants of vaccination uptake, and influenza vaccine effectiveness in preventing deaths and hospital admissions in the elderly population; Treviso, Italy, 2014/2015-2016/2017 seasons

“…44 During the following 2015/16 season, the co-circulation of A and B viruses was observed with a lower IVE estimate for influenza A(H1N1)pdm09, with respect to previous season due to the emerging genetic variant 6B.1. 45,46 In Veneto Region, most ILI and SARI cases were infected with A/H3N2 virus. 47 Moreover, during this season, the antigenic match between circulating strains (Victoria lineage) and vaccine composition (Yamagata lineage) did not fit for B.…”

Influenza Vaccine Effectiveness: New Insights and Challenges

“…Pooled VE against A(H1N1)pdm09 was 67% with low heterogeneity between estimates between 2009 and 2015 (Belongia et al 2016). However, VE against A(H1N1)pdm09 in Canada, Europe, and the United States was low (43%, 33%, and 45%, respectively) in 2015-2016 compared with prior postpandemic seasons in each region (Jackson et al 2017;Skowronski et al 2017b;Kissling et al 2018). The lower VE against A(H1N1)pdm09 was attributed to emergence of a genetic variant (6B.1), and this led to an update of the A(H1N1) vaccine component for the first time since the pandemic virus emerged (see who.int/influenza/vaccines/ virus/recommendations/2017_south/en/).…”