Influenza subtype-specific maternal antibodies protect offspring against infection but inhibit vaccine-induced immunity and protection in mice.

Following influenza A virus (IAV) infection or vaccination during pregnancy, maternal antibodies are transferred to offspring in utero and during lactation. The age and sex of offspring may differentially impact the transfer and effects of maternal immunity on offspring. To evaluate the effects of maternal IAV infection on immunity in offspring, we intranasally inoculated pregnant mice with sublethal doses of mouse-adapted (ma) H1N1, maH3N2, or media (mock) at embryonic day 10. In offspring of IAV-infected dams, maternal subtype-specific antibodies peaked at postnatal day (PND) 23, remained detectable through PND 50, and were undetectable by PND 105 in both sexes. When offspring were challenged with homologous IAV at PND 23, both male and female offspring had greater clearance of pulmonary virus and less morbidity and mortality than offspring from mock-inoculated dams. Inactivated influenza vaccination (IIV) against homologous IAV at PND 23 caused lower vaccine-induced antibody responses and protection following live virus challenge in offspring from IAV than mock-infected dams, with this effect being more pronounced among female than male offspring. At PND 105, there was no impact of maternal infection status, but vaccination induced greater antibody responses and protection against challenge in female than male offspring of both IAV-infected and mock-inoculated dams. To determine if maternal antibody or infection interfered with vaccine-induced immunity and protection in early life, offspring were vaccinated and challenged against a heterosubtypic IAV (i.e., different IAV group than dam) at PND 23 or 105. Heterosubtypic IAV maternal immunity did not affect antibody responses after IIV or protection after live IAV challenge of vaccinated offspring at either age. Subtype-specific maternal IAV antibodies, therefore, provide protection independent of offspring sex but interfere with vaccine-induced immunity and protection in offspring with more pronounced effects among females than males.