The makers of the nasal spray version of the flu vaccine say now they know why it has failed to protect young U.S. children against swine flu — fragile doses got too warm.
The AstraZeneca FluMist vaccine works well for most flu strains, but small studies found it didn’t work very well against the swine flu bug that first emerged in 2009. Swine flu has returned each year since but wasn’t a big player this flu season.
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