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Notice to Readers: SARS, Influenza, and Use of Influenza Vaccine

CDC supports and emphasizes the use of influenza vaccination for reducing influenza infections and their associated complications. CDC does not recommend influenza vaccination for the primary purpose of reducing the number of persons who might be evaluated for severe acute respiratory syndrome (SARS).

Influenza vaccine is effective only against influenza virus infection and is the best option for preventing influenza and its complications. These complications occur most often in children aged <24 months, persons aged >65 years, and those of any age who have certain medical conditions placing them at high-risk for having complications from influenza infection.* Annual vaccination is recommended for persons at high risk aged >6 months and for persons in other target groups, including family members and other close contacts of high-risk persons, those aged 50--64 years, and health-care workers. Vaccination is encouraged, when feasible, for children aged 6--23 months and for their household contacts and out-of-home caregivers. Influenza vaccination of health-care workers is especially important for reducing transmission of influenza viruses to patients with high-risk conditions in hospital and other health-care settings and for protecting the health-care workforce during the influenza season. Additional information about prevention and control of influenza is available at

On a population level, widespread use of the influenza vaccine will reduce the number of influenza cases and might decrease the number of persons with a febrile respiratory illness who are evaluated for SARS. However, such secondary benefits cannot be reliably anticipated. For example, the overall decrease in febrile respiratory illnesses would be minimal if circulating levels of influenza viruses are low or if other respiratory pathogens are actively circulating in a community.

Persons vaccinated against influenza can still have a febrile respiratory illness because influenza vaccine will not prevent infection by noninfluenza agents and the effectiveness of influenza vaccine is <100%. Therefore, receipt of influenza vaccination in a person who subsequently experiences a febrile respiratory illness does not eliminate influenza as a possible cause nor necessarily increase the likelihood that the illness is SARS.

* Persons at high risk include residents of chronic care facilities, persons with chronic pulmonary or cardiovascular disorders (e.g., asthma, chronic metabolic diseases, renal dysfunction, hemoglobinopathies, or immunosuppression), children receiving long-term aspirin therapy, and women who will be in the second or third trimester of pregnancy during the influenza season.

Use of trade names and commercial sources is for identification only and does not imply endorsement by the U.S. Department of Health and Human Services.

References to non-CDC sites on the Internet are provided as a service to MMWR readers and do not constitute or imply endorsement of these organizations or their programs by CDC or the U.S. Department of Health and Human Services. CDC is not responsible for the content of pages found at these sites. URL addresses listed in MMWR were current as of the date of publication.

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Safer, Healthier People

Morbidity and Mortality Weekly Report
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This page last reviewed 10/2/2003