Flu Vaccination May Be Effective Even When Circulating Strain Different From Vaccine

MedicalResearch.com Interview with:
Maryam Darvishian MSc
Department of Epidemiology, University Medical Center Groningen,
Unit of PharmacoEpidemiology and PharmacoEconomics (PE2),
Department of Pharmacy, University of Groningen,
Prof Edwin R van den Heuvel
Department of Epidemiology, University Medical Center Groningen,
University of Groningen, Groningen, Netherlands
Department of Mathematics and Computer Science,
Eindhoven University of Technology, Eindhoven, Netherlands

Medical Research: What is the background for this study?

Reply: In most developed countries, seasonal influenza vaccine is the standard care for elderly people, but there exists still discussions on whether vaccination is effective. Conducting RCT is not considered ethical and thus the main body of evidence comes from observational studies. Unfortunately, these studies (e.g. cohort studies) are susceptible to different sources of biases especially selection bias which makes it difficult to judge the effectiveness. In recent years test-negative design (TND) studies has been designed. It is a special type of case-control study which would limit the bias, due to similar health care-seeking behavior in cases and controls. The current study is a meta-analysis of TND case-control studies. It is the first meta-analysis of this type of studies and also the first meta-analysis that combined 35 studies for estimation of influenza vaccine effectiveness. More specifically, the meta-analysis assesses the influenza vaccine effectiveness against laboratory-confirmed influenza (LCI) among the elderly population.

Medical Research: What are the main findings?

Reply: Our findings show that influenza vaccine is effective against laboratory-confirmed influenza in community-dwelling elderly during regional and widespread influenza outbreaks. In cases where the vaccine matches the circulating virus, the vaccination is most effective, but it is also effective when the circulating virus does not match the strains in the vaccine.

Medical Research: What should clinicians and patients take away from your report?

Reply: Based on our findings, we believe that influenza vaccination uptake should increase among the elderly population.

Medical Research: What recommendations do you have for future research as a result of this study?

Reply: Influenza vaccine effectiveness is estimated annually. However, most of the studies do not adjust for covariates such as health status and possible co-morbidities in elderly population. Moreover, there is no individual patient data (IPD) meta-analysis that would take into account these important covariates and possibly provide a more accurate estimate of vaccine effectiveness. We believe that such studies should be conducted in the near future to verify the current estimates. Additionally, vaccines would improve when they would match the circulating virus, but viruses mutate and predicting the new strain is difficult. Vaccines that would improve on the match rate would be beneficial as well.


Effectiveness of seasonal influenza vaccine in community-dwelling elderly people: a meta-analysis of test-negative design case-control studies
Maryam Darvishian MSc,Maarten J Bijlsma MSc,Eelko Hak PhD,Prof Edwin R van den Heuvel PhD
The Lancet Infectious Diseases – 1 December 2014 ( Vol. 14, Issue 12, Pages 1228-1239 )
DOI: 10.1016/S1473-3099(14)70960-0