Oh, by the way . . . Should I get a flu shot while I'm pregnant?

November 1, 2007

The live attenuated vaccine should not be used in pregnant women given the small risk of viremia after administration.

THE INFLUENZA VACCINE is formulated yearly and is comprised of strains that are predicted to be common in the coming year's flu season, usually considered to be from October though March of the following year. Each year, an average of 34,000 Americans die from influenza and its complications.1 Rates of infection are highest among children, while deaths occur more frequently in the elderly (≥ 65), the very young (<2), and in persons with underlying medical conditions.1

The benefits far outweigh the risks

Pregnant women are at high risk for complications from influenza infection. In the epidemics of 1918–1919 and 1957–1958, an excessive number of influenza-associated deaths were noted among pregnant women.1 Pregnancy also appears to increase the risk for serious medical complications of influenza. Hospitalization rates for respiratory illnesses in pregnant women double during influenza season.5 These authors also reported an increase in delivery complications, although the rate of adverse perinatal outcomes and delivery complications did not increase in another study.6 In addition, infants and children under the age of 2 are at high risk for complications from the infection, and vaccinating family members of these groups, such as their mothers, will provide them with additional protection.

TWO FORMULATIONS of the influenza vaccine are currently available, one given intra muscularly and the other intranasally. The IM vaccine is a killed virus vaccine and the intranasal is a live attenuated viral vaccine. For this reason, the intranasal vaccine should not be used in pregnant women, given the (low) risk of viremia following administration of a live attenuated vaccine. The intranasal vaccine is approved for use in most children aged 5 and older and other adults. The IM vaccine is considered safe in all trimesters of pregnancy. The usual dose of the killed virus influenza vaccine is 0.5 mL IM. Children who have not been vaccinated previously should receive two doses of vaccine (doses separated by 6 weeks or more with the live attenuated vaccine, 4 or more weeks with the inactivated [killed virus] vaccine).1 There is no need for a booster vaccine in healthy adults.

Ideally, eligible patients should be vaccinated during the months of October and November. In many areas, vaccine may not be available until December or later, and should be administered as soon as it is available, as the influenza season extends through March.