During the 20th century, there were three pandemics, the most recent of which occurred in 1968. Pandemics are caused by the circulation of a new influenza virus and are accompanied by a very sharp increase in the number of cases and deaths, as well as an age distribution of the most affected populations that differs from that observed during seasonal flu epidemics. In France, an initial response plan was drafted in 1997. During its most recent revision, the Directorate General for Health (DGS) asked the French Institute for Public Health Surveillance (InVS) to study the potential impact of a pandemic and to compare the use of neuraminidase inhibitors (oseltamivir) with specific influenza vaccinations. (Introduction)