Helanterä I, et al. - In this work, researchers delineated two outbreaks of influenza A(H1N1) in immunocompromised patients to determine the efficacy of seasonal vaccination in these patients. Observations revealed the clinical efficacy of seasonal influenza vaccination with both a reduced risk of influenza infection and a trend towards reduced mortality in these immunocompromised patients. They identified several possible causes behind these two outbreaks that require continuous awareness in health care professionals to prevent further outbreaks.