In DepthInfectious Disease

Why is the flu vaccine so mediocre?

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Science  22 Sep 2017:
Vol. 357, Issue 6357, pp. 1222-1223
DOI: 10.1126/science.357.6357.1222

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With flu season around the corner in the United States and Europe, the push has begun once again to encourage people to receive their annual shots. But over the past few years, it's become increasingly clear that the level of protection offered by the vaccine varies widely each flu season, from 10% to 60%. And new research has revealed surprising reasons for its lackluster performance. For decades, it appeared that the vaccine had an efficacy of 70% to 90%, but scientists now know that's because they were using a misleading test—replaced in the 1990s—to assess whether it protected people. The traditional explanation for failure also has been revamped. The flu strains selected for the vaccine change each year based on what's in circulation, and scientists long blamed failure on mutations that occur in the circulating viruses in the 6–8 months that pass between the vaccine being manufactured and used. But these "mismatches" sometimes occur in years when there's solid protection, and some years with lots of failure have good matches. It turns out that other forces at work include mutations in the strain selected for the vaccine during the manufacturing process, which grows the virus in eggs. People's prior exposure to influenza also can bias their immune system toward a response that undermines that vaccine-triggered immunity. And the vaccine strain selection process itself relies heavily on the ferret animal model, which can mislead, too. There's an increasing call now to improve the vaccine and organize the research community to more collaboratively try to develop a "universal" flu shot that works against many strains and lasts for many years, if not a lifetime.