Influenza has significant potential for morbidity and mortality in pregnant women. Hospital admission rates for healthy pregnant women in the third trimester with influenza-related diseases are similar to those of persons with other high-risk conditions. The Advisory Committee of Immunization Practices recommends that pregnant women receive trivalent inactivated influenza vaccines during the influenza season. The inactivated form is the only influenza vaccine approved for use at any gestational age. Despite these recommendations, only about 12 percent of pregnant women are vaccinated. This low rate may be attributed to safety concerns regarding the vaccine, but studies have shown the influenza vaccine to be safe for the mother and fetus. Munoz and associates evaluated the safety of the influenza vaccine for pregnant women in the second and third trimesters.

The retrospective electronic database search included data from a U.S. multispecialty clinic over five years. Participants included women who had received inactivated influenza vaccines within six months of delivery, who were healthy, and who had uncomplicated singleton pregnancies. In addition, participants had at least one pre-natal care visit at the clinic, and their babies had at least one visit to the clinic. A matched comparison group was selected from the remainder of the database population. Outcomes included vaccination rate, safety and protection of the vaccine, and pregnancy outcomes.

The final analysis included 7,183 mother-infant pairs. The vaccination rate was 3.5 percent (252 women). Women with medical insurance were more likely to receive the vaccine than those who had Medicaid or no insurance. The mean gestational age at the time of vaccination was 26.1 weeks, and the average interval between vaccination and delivery was 13.9 weeks. There were no significant differences between the vaccination and control groups with regard to fever, pregnancy outcomes (i.e., preterm labor, preterm delivery, complicated delivery), or problems with the fetus (i.e., poor fetal growth). The infants’ medical conditions from birth to six months of age also were not significantly different between the two groups. No adverse events related to the vaccine were reported, and the analysis showed a trend toward a lower incidence of acute upper or lower respiratory tract illnesses in the vaccinated women during the peak influenza season.

The authors conclude that inactivated influenza vaccine provided during the second and third trimesters is safe. They add that safety concerns do not justify avoiding the use of the vaccine in pregnant women.