Grippe A (H1N1) 2009. Revue générale

Influenza A(H1N1) 2009 is an acute contagious respiratory infection caused by influenza A virus subtype H1N1 appeared in 2009 and responsible for a pandemic. The new virus, different from the avian virus H5N1, is a variant containing genes from several known viruses from porcine, avian and human origin. Appeared originally in the northern hemisphere, the epidemic wave reached early most countries, and up to 24% of the population in metropolitan France. It is characterized by a low mortality estimated at 0.04 to 0.2%, and by a benign, or even asymptomatic presentation. However, more severe clinical expression has been observed in some subgroups, carrying or not risk factors (young, pregnant women). The preexisting immunity in a significant proportion of the population, the remarkable stability of the virus, determination of early antigenic characteristics of the virus, the development and rapid availability of suitable vaccines, the efficacy of antiviral drugs, and health care system contributed to the control the morbidity and mortality of the first pandemic wave. Other virological, clinical and epidemiological investigations, are needed to identify all potential risk factors for severity and determine the role of mutation and the diffusion of pandemic and seasonal viruses, which may alter the virulence and transmissibility of influenza A(H1N1)v 2009.