Influenza virus infections cause significant morbidity and mortality throughout the world. Pregnant women and infants in the first year of life are high-risk populations, contributing to the estimated 5 million cases of severe influenza illness and more than 500 000 annual deaths worldwide.1,2 While influenza vaccination during pregnancy has been recommended in the United States for more than 60 years3 and supported by the World Health Organization,4 after the 2009 H1N1 influenza pandemic, maternal immunization against influenza became a global priority.5,6 The recommendation is primarily based on the need to protect pregnant women from complications of severe influenza, particularly in the third trimester of gestation.3,5-7 However, maternal influenza also poses a significant threat to the fetus and newborn, resulting in increased risk for preterm delivery and low birth weight, in addition to the infant’s higher risk for hospitalization and severe influenza illness in early life.5,8,9