Public health benefits of maternal influenza vaccination among pregnant women and infants <6 months in the United States, 2011-2020

BackgroundPregnant women and infants <6 months are at increased risk of influenza-associated complications. Maternal influenza vaccination during pregnancy has a strong safety record and is effective in reducing the risk of illness in these groups. We estimate influenza disease burden, and the burden prevented by maternal influenza vaccination, among pregnant women and their infants <6 months in the United States during the 2011/12-2019/20 influenza seasons. Methods and findingsWe applied a multiplier model and compartmental framework to data that included monthly influenza-associated hospitalizations among pregnant women and infants <6 months, influenza vaccination coverage among pregnant women, and influenza vaccine effectiveness. We estimated the number of influenza-associated hospitalizations and intensive care unit (ICU) admissions among pregnant women and infants <6 months, and the corresponding number prevented by vaccination. We also simulated alternative vaccination coverage scenarios to investigate whether increased and/or earlier influenza vaccination uptake each season could have prevented additional hospitalizations. From 2011/12-2019/20, we estimated that 2,670-10,000 influenza-associated hospitalizations and 76-486 ICU admissions occurred annually among pregnant women, and 3,960-13,100 hospitalizations and 457-1,830 ICU admissions occurred annually among infants <6 months. Influenza vaccination prevented an estimated 33-2,440 hospitalizations and 1-166 ICU admissions annually among pregnant women, and 29-1,350 hospitalizations and 4-178 ICU admissions annually among infants <6 months. We projected that increased influenza vaccination uptake would have prevented more hospitalizations among pregnant women than earlier vaccination, whereas the converse was true for infants <6 months. Together, we estimated increased and earlier vaccination uptake could have prevented an additional 12-942 influenza-associated hospitalizations annually among pregnant women and 17-1,010 hospitalizations annually among infants <6 months. ConclusionsOur findings suggest maternal influenza vaccination reduces disease burden among pregnant women and their infants <6 months who are too young to be vaccinated.