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Tuesday, July 16, 2013

Good news about the flu vaccine

Each year, the World Health Organization (WHO) makes an educated guess about which strains of influenza virus will be most prevalent in the upcoming flu season. Based on their recommendations, vaccine manufacturers mass produce that year’s flu vaccine. Sometime, the predictions are spot-on, but other times, there’s considerable mismatch between the vaccine and the circulating viruses. The good news is that it may not matter.

Researchers from universities and hospitals in Ontario, Canada scoured clinical trials to find people who had come down with the flu after being vaccinated for influenza. After narrowing down their search criteria to exclude studies without laboratory-confirmed influenza, proper placebo controls or full vaccination, the scientists ended up with 34 trials, covering 47 influenza seasons and involving nearly 95,000 participants.

Even when the vaccines did not match that year’s flu strains, the vaccines were considerably better than placebo at preventing influenza infection. A mismatched live-attenuated vaccine (nasal spray) reduced infection rates by 60% and an inactivated vaccine (shot, or jab) did so by 56%. In comparison, properly matched vaccines reduce the risk of contracting the flu by 77% and 65%, respectively.

This means that individuals should not shirk from getting vaccinated even if they hear that the current vaccine doesn’t match that season’s flu virus. It also means that communities will benefit from herd immunity when their members get vaccinated regardless of whether the WHO was correct in their predictions.

Tricco AC, Chit A, Soobiah C, Hallett D, Meier G, Chen MH, Tashkandi M, Bauch CT, & Loeb M (2013). Comparing influenza vaccine efficacy against mismatched and matched strains: a systematic review and meta-analysis. BMC medicine, 11 (1) PMID: 23800265.

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