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Mass vaccination campaigns always are shadowed by fears that reports will follow of serious vaccine side effects — either real or, more commonly, perceived. In the case of last year's rapid worldwide mobilization against the H1N1 “swine” flu, a giant study from China provides reassurance that the vaccine was safe.
In a passive surveillance system, physicians and other vaccine providers reported to a central authority all adverse events experienced by 90 million recipients of 2009–2010 H1N1 vaccine supplied by 10 Chinese manufacturers. Most reported adverse events — largely fever and local reactions — were minor. Among the more severe events were 11 cases of Guillain-Barré syndrome (onset, 0–80 days after vaccination), with an overall rate no…