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Roughly 1 in 5 unvaccinated people had the flu between 2006 and 2011, but only a quarter of them had symptoms, a study found. That could affect how the virus spreads.
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Young people are usually less likely to become seriously ill with flu, but this season looks like an exception to that rule. Blame the H1N1 strain. Even though the flu vaccine is less than perfect, getting a shot each year can make the illness less severe, doctors say.