Introduction: In April 2009 an influenza outbreak caused by a new virus, influenza A (H1N1), started in the Mexican-American border. Later this outbreak became pandemic but not as severe as initially thought; immunization programs were developed, and vaccines used led to vaccine adverse events (VAE). Objectives: To assess a possible relationship between spontaneously reported VAE and influenza A H1N1 vaccination in an institute’s healthcare workers. Design: Prospective and descriptive study based on spontaneous notification. Setting: Instituto Nacional de Salud headquarters, Lima, Peru. Participants: Healthcare workers. Methods: Spontaneously notified VAE were recorded in specially designed sheets. An algorithm was used in order to assess a cause-effect relationship. Main outcome measures: Influenza A(H1N1) vaccination adverse events. Results: There were three spontaneous reports in 14...