Effectiveness of influenza vaccine in the Netherlands:predominant circulating virus type and vaccine match are important conditions

OBJECTIVE: To investigate the relationship between circulating influenza virus A types and subtypes and influenza B lineages, their match with the vaccine and the effectiveness of the influenza vaccine (IVE).DESIGN: Test negative case control study.METHOD: We used data from the Dutch Sentinel Practices of the Netherlands Institute for Health Services Research (NIVEL) Primary Care Database. Participating general practitioners took nose and throat swabs for viral studies from patients with influenza-like illness or another acute respiratory infection. Cases were those patients whose samples were positive for an influenza virus and controls were those whose samples were negative for influenza virus. We determined the IVE of 11 influenza seasons 2003/2004 to 2013/2014, for all seasons together and stratified by influenza virus type and to vaccine match or mismatch.RESULTS: Over all seasons, the IVE was 29% (95% CI:11-43). In seven of the 11 seasons there was a mismatch between vaccine and circulating virus type. The IVE was 40% (95% CI: 18-56) for those seasons in which there was a vaccine match, and 20% (95% CI: - 5-38) for seasons with a mismatch. When the influenza A/H3N2 virus was dominant, the IVE was 38% (95% CI: 14-55). The IVE against the influenza virus A/H1N1, A/H1N1/pdm09 and against both influenza B lineages was 77% (95% CI: 37-92), 47% (95% CI: 22-64) and 64% (95% CI: 50-74), respectively.CONCLUSION: The IVE was particularly low when there was a mismatch between the vaccine and the circulating virus type and when A/H3N2 was the dominant influenza subtype.