Every year, the government takes a gamble on the strains of flu most likely to cause the greatest number of infections in the coming flu season, and commissions a vaccine based on those strains. The US Food and Drug Administration announced Monday (July 18) that this year’s lucky numbers will be the same as last year’s, since those strains are still some of the most widely circulating and most frequently associated with disease.

The viruses used are chosen by 136 influenza surveillance centers around the world, whose samples help determine the most prevalent circulating strains. This year’s chosen ones include the H1N1 flu strain responsible for the "swine flu" pandemic of 2009, as well as another type A virus, and one of the two prevalent B type strains.

Although the vaccine composition is the same, the CDC still recommends those who took it last year to get...

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