[Basic epidemiological characteristics of influenza infection].

Influenza is a relatively serious infection that affects hundreds of thousands of people every year in the Czech Republic alone, with unnecessary deaths as a possible outcome. Vaccination against influenza is the most important preventive measure. The highest incidence of seasonal influenza is reported in school-age children and young adults while the highest mortality is observed among the elderly. Pandemic influenza may significantly differ from seasonal influenza in these two aspects. Other epidemiological characteristics of seasonal influenza are presented and compared with those of 2009 pandemic A/H1N1 ("Mexican") influenza that caused the first pandemic of the 21st century.