Systematic Literature Review of Maternal Antibodies in Human Milk Following Vaccination During Pregnancy or Lactation Tetanus, Pertussis, Influenza and COVID-19

Background: Human milk (HM) contributes to infant disease protection through transfer of numerous bioactive molecules, including antibodies, though the mechanisms that determine HM antibody transfer and disease prevention in the infant are not fully understood. Even less is known about the transfer of, and infant protection afforded by, vaccine-induced HM antibodies following vaccination during pregnancy or lactation. This systematic literature review aimed to summarize published evidence on the presence, duration and function of HM antibodies against pertussis, influenza and coronavirus disease 2019 (COVID-19) induced by vaccination during pregnancy or lactation and the associated protection against infant illness and to identify gaps to guide future research in this area. Methods: Literature searches were conducted on September 15, 2023, in MEDLINE and Embase for articles published since January 2000. Results: Eighteen studies reporting vaccine-induced antibodies in HM or protection against infant illness were included. The collective evidence supports increased and sustained HM antibody levels following influenza and COVID-19 vaccination while antipertussis HM antibody levels remained elevated for only approximately 4 weeks postvaccination. COVID-19 booster vaccination during pregnancy was found to prolong the half-life of immunoglobulin G antibodies in HM relative to the COVID-19 primary vaccination series. Only 2 studies evaluated illness among breastfed infants born to mothers vaccinated during pregnancy; however, neither distinguished the independent effects of transplacental transfer of vaccine-induced antibodies, HM transfer of vaccine-induced antibodies and HM transfer of naturally acquired antibodies. Conclusions: HM antibody levels are increased following pertussis, influenza and COVID-19 vaccination during pregnancy or lactation. However, the limited evidence base precludes conclusions about any incremental benefit of breastfeeding following vaccination during pregnancy versus the benefit of breastfeeding alone and studies designed to address this question are needed to inform vaccine policy.