World-wide surveillance of influenza.

Influenza epidemics and pandemics resulting in excess mortality are due to various influenza viruses, in which through the accumulation of mutations the structure changes. A world-wide surveillance has been set up for early detection of new influenza virus strains and of epidemics or pandemics resulting thereof. Basing on such data the World Health Organisation (WHO) issues recommendations to Public Health authorities on the most efficient means for prevention.