Influenza--its impact and control.

Influenza is an underestimated public health problem. Epidemics spread rapidly from country to country and may affect as many as 500 million people across the world in a moderate influenza year. The disease, particularly influenza A, kills and the new influenza viruses which appeared in 1957 (Asian influenza) and 1968 (Hong Kong) are estimated to have caused at least 100,000 deaths in the United States of America. Deaths from influenza also occur in years when there is no new virus; at least 10,000 excess deaths have been documented in the United States during each of 18 different epidemics recorded from 1957 to 1985. Although most deaths are among the elderly, influenza occurs in all age groups with repercussions in schools and work places, and on hospital resources, at a high cost to society. As many as 79-80% of influenza cases can be prevented when the virus inducing the outbreak and the virus used in the influenza vaccine are closely related. Preventing 80% of cases would correspond in the United States to a saving of US $2.5 billion. People at the greatest risk of influenza-related complications are adults and children with chronic disorders of the pulmonary or cardiovascular systems, residents of nursing homes and of facilities for patients with chronic medical conditions. Other priority groups for vaccination are those at moderate risk of influenza-related complications such as healthy elderly persons, people with chronic metabolic diseases, children and teenagers on long-term aspirin therapy. Groups potentially capable of transmitting influenza to high-risk persons should also be vaccinated.(ABSTRACT TRUNCATED AT 250 WORDS)