The adverse events of influenza A (H1N1) vaccination and its risk factors in healthcare personnel in 18 military healthcare units in Korea

In this study, we characterized adverse events related to influenza A (H1N1) vaccination and studied the factors that influence the occurrence of these events. A total of 4,302 personnel in 18 military healthcare units in Korea received 0.5 ml of inactivated H1N1 vaccine. The study questionnaires were answered by 3,939 (91.6z) personnel, at both 2 weeks and 4 weeks after vaccination. Among these subjects, 3,531 (82.1z) who responded to all questions in the questionnaire were studied. After immunization, military doctors were ordered to report the occurrence of any adverse event related to the vaccine for 2 months. According to the responses of the subjects, the most prevalent events were fatigue (11.3z), pain at the injection site (8.38z), and myalgia (6.97z). Female gender, being in the age range of 20-49 years, obesity, regular alcohol consumption, and comorbidity, but not smoking status or pregnancy, were related to a high incidence of local or systemic adverse events after H1N1 vaccination. A total of 14 cases of adverse events were reported by the military doctors. In most reported cases, the subjects had fever in addition to the primary adverse event, and one patient was diagnosed with pneumonia. In conclusion, the overall burden of adverse events related to influenza A (H1N1) vaccination was not inconsequential, but most symptoms were mild. Female gender, middle-age range of 20-49 years, obesity, regular alcohol consumption, and comorbidity were risk factors for the occurrence of adverse events after H1N1 vaccination.