Immune response during lactation after anti-SARS-CoV2 mRNA vaccine

Importance: Data regarding efficacy and safety of anti-COVID-19 mRNA vaccines during lactation is needed to address vaccination guidelines, ease vaccine hesitancy concerns, and inform public health strategies for this population. Objective: To determine whether anti-COVID-19 mRNA-based vaccines administered during lactation illicit an immune response or the transfer of anti-SARS-CoV2 antibodies into human milk. Design: Plasma and milk samples were collected from a prospective cohort of lactating individuals who received the mRNA-based vaccines for COVID-19 and from individuals who recovered from COVID-19 infection. Setting: Ambulatory or during postpartum hospitalization. Participants: We report results from lactating participants who received the mRNA-1273 (Moderna, n=9) or the BNT162b2 (Pfizer, n=14) vaccine or recovered from natural SARS-CoV-2 infection (n=3). Interventions and Exposures: Anti-COVID-19 mRNA vaccination (BNT-162b2 and mRNA-1273) or natural SARS-CoV-2 infection. Main Outcome(s) and Measure(s): Plasma and milk samples were collected from lactating individuals before first vaccine dose, on the day of the second dose, and 4 weeks after the second dose. Maternal plasma was evaluated for vaccine-derived IgM and IgG antibodies. Human milk was evaluated by ELISA for vaccine-induced IgA antibodies specific for SARS-CoV-2. Results: Twenty-three lactating individuals were recruited for this study. Levels of IgG and IgM were significantly increased in plasma samples on the day of the second vaccine dose (post vaccine 1), when compared to pre-vaccine samples. In addition, plasma IgG levels 4 weeks after second vaccine dose were significantly higher than plasma IgG levels pre-vaccine or on the day of the second dose. In addition, our results show transfer of anti-SARS-CoV2-Receptor Binding Domain (RBD) IgA antibodies to human milk, 3-4 weeks after each dose of the COVID-19 mRNA vaccines (BNT-162b2 and mRNA-1273). The levels of anti-SARS-CoV2-RBD IgA antibody in milk of vaccinated individuals were not significantly different from levels among participants who experienced SARS-CoV-2 infection. Conclusions and Relevance: Administration of anti-COVID-19 mRNA vaccines during lactation leads to increased anti-SARS-CoV2 IgM and IgG levels in the plasma of lactating mothers and increased anti-SARS-CoV2-RBD IgA levels in human milk. Lactating women who receive the vaccine should continue breastfeeding their infant human milk to allow continuing transfer of anti-SARS-CoV-2 IgA antibodies to the neonate. Additional studies are needed to evaluate the effect of these vaccines on lactation outcomes and infant health.