Influenza Facts

• Influenza A (H1N1) viruses, influenza A (H3N2) viruses, and influenza B viruses have been in global circulation since 1977.

• The 2000-2001 trivalent vaccine virus strains are A/Moscow/10/99 (H3N2)-like, A/New Caledonia/20/99 (H1N1)-like, and B/Beijing/184/93-like strains.

• Immunity to the surface antigens, especially hemagglutinin, reduces the likelihood of infection and severity of disease if infection occurs.

• The incubation period averages two days. People can be infectious the day before symptoms begin and remain infectious for five days after the onset of illness. Children can be infectious for a longer period.

• Symptoms include fever, myalgia, headache, severe malaise, nonproductive cough, sore throat, and rhinitis.

• An average of 114,000 excess hospitalizations per year are attributed to influenza.

Source: Prevention and Control of Influenza: Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR 2000; 49(RR-03):1-38.