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Current recommendations to vaccinate pregnant women against influenza aim to protect both the women (in whom pregnancy induces immunosuppression) and their infants. Investigators conducted two randomized trials in South Africa in which 2116 HIV-uninfected women and 194 HIV-infected women between 20 and 36 weeks of pregnancy received intramuscular inactivated trivalent influenza vaccine or placebo. Mothers and infants were followed for 24 weeks postnatally for respiratory illness and virologically confirmed influenza.
Among HIV-negative women, those who received the influenza vaccine were less likely to develop influenza than those who received placebo (rates of confirmed influenza, 1.8% vs. 3.6%; P=0.01), as were their infants (1.9% vs. 3.6%; P=0.01). Vaccinated HIV-seropositive women also benefited over those who received placebo (7.0% vs. 17.0%; P=0.05). However, infants born to vaccinated HIV-seropositive women did not benefit (5.0% and 6.8%; P=0.6).
Madhi SA et al. Influenza vaccination of pregnant women and protection of their infants. N Engl J Med 2014 Sep 4; 371:918. (http://dx.doi.org/10.1056/NEJMoa1401480)
Comment
This is the second large trial to show benefit to pregnant women and their infants from influenza immunization during the second half of pregnancy. Although this strategy has been recommended in the U.S. for several years, only about half of pregnant women are vaccinated (MMWR 2013; 62:787). Success depends on clinicians both endorsing the vaccine's use and providing it as part of routine prenatal care.