[Which response against the next influenza pandemic?].

An influenza pandemic is caused by the emergence or the reoccurrence as well as the explosive spreading of a new influenza A virus in an immunologically unprotected population. During this century, three severe pandemics occurred: the Spanish Flu in 1918, the Asian Flu in 1957 and the Hong Kong Flu in 1968. The first one was responsible for 20 millions deaths. A future pandemic is very likely to occur but we cannot predict when it will happen. The mechanism of emergence of a new virus is totally different of the one observed during the annual interpandemic outbreaks. Since the severity of a pandemic virus is unpredictable, action plans must be designed to avoid over-reaction to harmless influenza viruses and at the same time to be adequate in dealing with a threatened new pandemic. Thus these two situations need different control and prevention plans.