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Case-control studies, using a “test-negative design”, can be used to assess the effectiveness of seasonal influenza vaccine while limiting selection bias. They compare vaccine status between patients presenting with influenza-like symptoms who test positive for influenza with laboratory tests and those who test negative.
A meta-analysis of 35 such studies was undertaken by Edwin van den Heuvel, from Eindhoven University, the Netherlands, and colleagues. All studies included high-risk people aged 60 years and older.
The results, reported in The Lancet Infectious Diseases (online, 6 November 2014)[1]
, reveal that vaccination was effective during regional and widespread outbreaks, irrespective of whether the vaccine matched the circulating viruses. Vaccination was also effective during sporadic outbreaks but only when the vaccine matched.
“Efforts should be renewed worldwide to further increase uptake of the influenza vaccine in the elderly population,” say the researchers.
References
[1] Darvishian M, Bijlsma MJ, Hak E, et al. Effectiveness of seasonal influenza vaccine in community-dwelling elderly people: a meta-analysis of test-negative design case-control studies. The Lancet Infectious Diseases 2014. doi: 10.1016/S1473-3099(14)70960-0 (accessed on 6 November 2014).
