Pandemic influenza A (H1N1) 2009: the experience of the first six months

After a break of 41 years, 2009 saw the first influenza pandemic of the 21st century caused by a triple-reassortant influenza A (H1N1) virus. The current estimated case fatality rate is lower than that of previous influenza pandemics, but this may change as the pandemic evolves. Illness frequently occurs in previously healthy, young adults with a wide range of clinical presentations. The majority of circulating pandemic viruses remain susceptible to neuraminidase inhibitors, although all strains are intrinsically resistant to the adamantanes. Monovalent vaccines against the pandemic strain are available in both live attenuated and inactivated forms. This review aims to summarise important virological, epidemiological and clinical aspects of the pandemic influenza A (H1N1) virus for physicians and other clinical personnel.