Influenza vaccine effectiveness during the 2012 influenza season in Victoria, Australia: Influences of waning immunity and vaccine match

Abstract

Vaccine effectiveness may wane with increasing time since vaccination. This analysis used the Victorian sentinel general practitioner (GP) network to estimate vaccine effectiveness for trivalent inactivated vaccines in the 2012 season. A test‐negative design was used where patients presenting to GPs with influenza‐like illness who tested positive for influenza were cases and noncases were those who tested negative. Vaccination status was recorded by GPs. Vaccine effectiveness was calculated as (1‐odds ratio) × 100%. Estimates were compared early versus late in the season and by time since vaccination. Virus isolates were assessed antigenically by hemagglutination inhibition assay in a selection of positive samples and viruses from healthy adults who experienced a vaccine breakthrough were analyzed genetically. The adjusted vaccine effectiveness estimate for any type of influenza was 45% (95% CI: 8,66) and for influenza A(H3) was 35% (95% CI: −11,62). A non‐significant effect of waning effectiveness by time since vaccination was observed for A(H3). For those vaccinated <93 days of presentation vaccine effectiveness was 37% (95% CI: −29,69), while for those vaccinated ≥93 days before presentation it was 18% (95% CI: −83,63). Comparison of early versus late in the season estimates was very sensitive to the cut off week chosen for analysis. Antigenic data suggested that low vaccine effectiveness was not associated with poor vaccine match among the A(H3) viruses. However, genetic analysis suggested nucleotide substitutions in antigenic sites. In 2012, the trivalent influenza vaccine provided moderate protection against influenza and showed limited evidence for waning effectiveness. Antigenic and genetic data can provide additional insight into understanding these estimates. J. Med. Virol. 86:1017–1025, 2014. © 2013 Wiley Periodicals, Inc.

Predicting clinical severity based on substitutions near epitope A of influenza A/H3N2

“…Similar epidemiological findings have been reported in China (Cai et al, 2014). In comparison, the subclade 3A viruses were detected at a prevalence of 13-40% in the 2011-2012 influenza seasons in Australia and European countries (Fantoni et al, 2014;Pariani et al, 2013;Sullivan et al, 2014). Although these three subclades (3A, 3B and 3C) were antigenically indistinguishable (WHO, 2012), the variety of different circulating subclades in different regions around the world suggests that a seasonal vaccine targeted at more regionally circulating seasonal viruses may provide more optimum protection for the local populations.…”

I-MOVE multicentre case–control study 2010/11 to 2014/15: Is there within-season waning of influenza type/subtype vaccine effectiveness with increasing time since vaccination?

“…An Australian study reported a decline in VE, but it was sensitive to the cut-off chosen [33]. In this study we modelled time since vaccination as a spline, which provides added value to the categorical approach.…”

Influenza vaccine effectiveness: Maintained protection throughout the duration of influenza seasons 2010–2011 through 2013–2014

“…Previous studies have found declines in VE for influenza A (H3N2) over time, with their VE estimates showing non-significant protection from the vaccine after several months [3][4][5][6][7] or evidence for increased infection with longer time since vaccination [14]. However, some of these studies had relatively small sample sizes and thus may have been underpowered to identify statistically significant VE even when it existed.…”

“…Yearly revaccination is necessary because circulating strains and/or vaccine composition change every influenza season. Additionally, previous studies have found that influenza vaccine effectiveness (VE) declines over time since vaccination in some populations does not provide significant protection in most cases after 90-120 days [3][4][5][6][7]. Many factors impact VE estimates and speed of decline -including age, comorbidities, herd immunity, use of adjuvants, type of vaccine administered (live attenuated or inactivated), prior natural influenza exposure, prior influenza vaccination, antigenic drift, and study design [6,[8][9][10][11][12][13].…”