Influenza is not just a common cold. It is caused by a virus of the same name, prevails in the cold season and afflicts annually a considerable part of the population. The decrease of other infectious diseases is one of the reasons why the flu is nowadays considered as a not so innocent disease, responsible for an excess mortality of several hundreds of citizens per year in the Netherlands. There is a - annually revised - rather acceptable vaccine available that is still applied too little. The last years, virologists warn for the possibility that a mutant virus might create a pandemic comparable to the Spanish Flu of 1918.