Does getting the flu shot each year make the vaccine less effective?

News Release

25 Aug 2017

New research from Public Health Ontario (PHO) scientists found that effectiveness of influenza vaccines does not decrease with getting the vaccination two years in a row.

The paper is titled The impact of repeated vaccination on influenza vaccine effectiveness: a systematic review and meta-analysis and is published in BMC Medicine. PHO scientists Dr. Bryna Warshawsky and Dr. Jeff Kwong led a systematic review and meta-analysis of 20 research articles looking at the impact of repeated influenza vaccination over two seasons on vaccine effectiveness. The results suggest that receiving the influenza vaccine in both of the two years provides similar protection against influenza compared to if a person is just vaccinated in the current year. From the patient’s perspective, vaccination in the current year is generally the best option regardless of whether or not they were vaccinated in the prior year. 

The researchers say the findings should provide reassurance that for most influenza seasons, influenza vaccine effectiveness is not lessened for individuals who have been vaccinated the previous year. However, they also say additional research is needed to look at the impact of receiving influenza vaccines repeatedly over many years.

A blog post by the researchers accompanied the release of the research paper in BMC Medicine.

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Updated 25 Aug 2017