Maternal Vaccination Decreases Risk of Influenza in Mothers and Their Infants

EBM Focus - Volume 9, Issue 37

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Reference: N Engl J Med 2014 Sep 4;371(10):918 for women without HIV infection (level 1 [likely reliable] evidence) for women with HIV infection (level 2 [mid-level] evidence)

Pregnant women are at increased risk of severe influenza from their second trimester until the early postpartum period, and are considered a priority group for receiving seasonal influenza vaccine by the World Health Organization (Weekly Epidemiological Record PDF) and the Centers for Disease Control and Prevention (MMWR Recomm Rep 2013 Sep 20;62(RR-07):1 full-text). However, data on the efficacy of influenza vaccination in this population is limited, particularly data showing a protective effect on infants after birth. Two recent randomized trials from South Africa evaluated the efficacy of trivalent inactivated influenza vaccination in 2,116 pregnant women not infected with HIV, in 194 pregnant women with HIV infection, and in their newborns up to 24 weeks after birth.

In pregnant women without HIV infection, the rate of laboratory-confirmed influenza was 1.8% with influenza vaccine vs. 3.6% with placebo (p = 0.01). Similarly, among infants born to vaccinated mothers, confirmed influenza infection rates were 1.9% with influenza vaccine vs. 3.6% with placebo (p = 0.01). In pregnant women infected with HIV, the rates of laboratory-confirmed influenza with vaccine vs. placebo were 7% vs. 17% (p = 0.05) in mothers and 5% vs. 6.8% among their infants (not significant). There were no significant differences between the influenza group and the placebo group for rates of nonspecific influenza-like illness or for respiratory illnesses in general, irrespective of HIV infection status.

The protective effect of inactivated influenza vaccine for infants of vaccinated mothers observed in these new trials is consistent with a previous trial conducted in Bangladesh. This previous trial of 340 women found that a similar maternal vaccination reduced laboratory-confirmed influenza cases in infants followed for 24 weeks compared to maternal vaccination with pneumococcal vaccine (N Engl J Med 2008 Oct 9;359(15):1555). This newer and larger trial further solidifies this protective effect in mothers without HIV infection and their infants. It also suggests benefit for HIV-infected mothers as well, a population that may be particularly vulnerable to infection.

For more information see the Influenza in pregnancy topic in DynaMed.