Children can be infectious for a longer period. Uncomplicated influenza is characterized by the abrupt onset of fever, myalgia, headache, severe malaise, nonproductive cough, sore throat, and rhinitis. In some people, influenza can exacerbate underlying medical conditions such as pulmonary or cardiac disease or lead to secondary bacterial pneumonia or primary influenza viral pneumonia. Although drugs are becoming available to treat influenza, the disease vaccines remain the primary method for preventing influenza and its complications. When vaccine and epidemic strains are well-matched, achieving high vaccination rates, particularly in nursing home, day care, school, and health care environments, can reduce the risk of outbreaks by inducing widespread immunity.
Influenza vaccine contains two type A and one type B influenza virus strains.
These antibody titers are protective against illness caused by strains similar to those in the vaccine. The effectiveness of influenza vaccine depends primarily on the age and immunocompetence of the vaccine recipient and the degree of similarity between the viruses in the vaccine and those in circulation. The elderly and people with certain chronic diseases, such as heart disease, asthma, and diabetes, might develop lower postvaccination antibody titers than healthy adults and remain susceptible to influenza-related upper respiratory tract infection. For these individuals, the vaccine still can be effective in preventing secondary complications and reducing the risk of influenza-related hospitalization and death. Among elderly persons residing in nursing homes, influenza vaccine is most effective in preventing severe illness, secondary complications, and deaths.