Omer SB, Clark DR, Madhi SA, et al. - Via performing a pooled analysis of three randomized controlled trials conducted in Nepal (2011–2014), Mali (2011–2014), and South Africa (2011–2013), researchers investigated the vaccine efficacy of maternal influenza immunization against maternal and infant PCR-confirmed influenza, duration of protection, and the effect of gestational age at vaccination on vaccine efficacy, birth outcomes, and infant growth up to 6 months of age. Pregnant women, gestational age 17–34 weeks in Nepal, 28 weeks or more in Mali, and 20–36 weeks in South Africa, were randomly assigned to receive trivalent inactivated influenza vaccine (IIV) (study group) in all three trials, or to receive saline placebo in Nepal and South Africa or quadrivalent meningococcal conjugate vaccine in Mali (control group). Inclusion of 10,002 women and 9,800 liveborn infants was done. Per findings, IIV administered in pregnancy was linked with an overall efficacy of 35% for PCR-confirmed influenza among infants younger than 6 months of age. Greater protection against infant influenza was noted in the first 2 months of life, with 56% efficacy, but after 4 months of age, the vaccine did not show efficacy. Per previous reports of the individual RCTs, there were heterogonous estimates of maternal IIV efficacy in infants, with estimates ranging from 63% in Bangladesh to 30% in Nepal. Such heterogeneity in efficacy estimates may be because of the fact that the effects of influenza vaccination vary by time and location. An overall 35% efficacy and 56% efficacy among infants younger than 2 months could, however, have substantial public health implications, as young infants are at risk of experiencing more severe disease compared with older children. Lower vaccine efficacy was evident among women who were vaccinated earlier than the median gestational age at vaccination (29 weeks) than those vaccinated later.  Infants born to mothers vaccinated before or after 29 weeks gestation had similar efficacy. No overall association was observed between maternal vaccination and low birthweight, stillbirth, preterm birth, and small for gestational age. The evaluation of efficacy for women vaccinated before 29 weeks gestational age might have been underpowered, because the point estimate indicates that there might be efficacy despite wide CIs.