Pandemic planning.
During the previous century, three influenza A pandemics occurred with a variable severity. The two latter were explained by a genetic re-assortment and false alarms without pandemic spread were observed later by the same mechanism or by direct animal infection. The likelihood that such an event occurs again is high and each country has to be prepared for facing what could be a catastrophe. The last event in Hong Kong in 1997 where six persons died, has allowed refining the definitions and phasing a pandemic threat from the moment that a novel virus is discovered. WHO implemented 50 years ago a large network of surveillance with five collaborating centres, including the animal influenza centre of Memphis, and 110 national influenza centres. These centres are encouraged to prepare or improve a national contingency plan that could reduce importantly medical and socio-economic consequences of an influenza A pandemic. Countries or regions are recommended to use these guidelines that provide a framework for preparing an appropriate and proportionate response.