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Am Fam Physician. 1998;57(4):858

A new intramuscular trivalent influenza vaccine is available for the current influenza season. Except for one new antigen (H1N1 antigen), the antigen mix in the current vaccine is the same as last year's. Although it was anticipated that a new nasal spray flu vaccine would be available this year, it has not yet received approval from the U.S. Food and Drug Administration. Consultants from the Medical Letter on Drugs and Therapeutics review current data for the new influenza vaccine.

Influenza vaccination is recommended for elderly and other high-risk patients, their household contacts and health care personnel who may be in contact with them. The vaccination of healthy working adults and children may prevent household spread of the disease. Pregnant women can be vaccinated safely. There is an increased risk of influenza complications in women in the second and third trimesters of pregnancy.

Outbreaks of influenza usually reach a peak between late December and early March and may continue into the spring in some areas. Following vaccination, protection from influenza generally begins one to two weeks after injection and may last six months or longer. Elderly persons may not maintain serum antibody levels for six months and may fall below protection levels in four months or less. The optimal time for influenza vaccination is from October through mid-November, but vaccination any time from September to the end of the influenza season is appropriate.

Dosage recommendations differ for adults and children. A single intramuscular 0.5-mL dose of the vaccine is recommended for adults and for children who are at least three years of age. Children from six to 35 months of age should receive a dose of 0.25 mL. Children younger than nine years of age receiving the vaccine for the first time should receive two doses at least four weeks apart.

Because the influenza vaccine is made from inactivated virus grown in eggs, hypersensitivity reactions can occur, although they are rare. Occasionally, soreness may persist for one to two days at the injection site. Fever, myalgia and malaise can last one or two days but usually occur in young patients with no previous exposure to influenza antigens. Some reactions in children can be averted by administering split-virus and purified-surface-antigen formulations (see the accompanying table).

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Consultants from the Medical Letter recommend influenza vaccination for high-risk persons and the elderly, their household contacts and health care workers. Adverse reactions are rare and can usually be averted by altering the dosage recommendations.

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