Adverse events following influenza A (H1N1) 2009 monovalent vaccines reported to the Vaccine Adverse Event Reporting System, United States, October 1, 2009-January 31, 2010.

The United States (US) influenza A (H1N1) 2009 monovalent (2009-H1N1) vaccination program began in October 2009. Reports to the vaccine adverse event reporting system (VAERS), a US spontaneous reporting system, were reviewed to identify potential rare events or unusual adverse event (AE) patterns after 2009-H1N1 vaccination. The adverse event profile after 2009-H1N1 vaccine in VAERS (∼10,000 reports) was consistent with that of seasonal influenza vaccines, although the reporting rate was higher after 2009-H1N1 than seasonal influenza vaccines, this may be, at least in part, a reflection of stimulated reporting. Death, Guillain-Barré syndrome and anaphylaxis reports after 2009-H1N1 vaccination were rare (each <2 per million doses administered).