SARS-CoV-2 infection versus vaccination in pregnancy: Implications for maternal and infant immunity

Background: SARS-CoV-2 infection has been associated with adverse maternal and neonatal outcomes, yet uptake of SARS-CoV-2 vaccines during pregnancy and lactation has been slow. As a result, millions of pregnant and lactating women and their infants remain susceptible to the virus. Methods: We measured Spike-specific immunoglobulin G (anti-S IgG) and A (anti-S IgA) in serum and breastmilk (BM) samples from 3 prospective mother-infant cohorts recruited in two academic medical centers. The primary aim was to determine the impact of maternal SARS-CoV-2 immunization vs infection and their timing on systemic and mucosal immunity. Results: The study included 28 mothers infected with SARS-CoV-2 in late pregnancy (INF), 11 uninfected mothers who received 2 doses of the BNT162b2 vaccine in the latter half of pregnancy (VAX-P) and 12 uninfected mothers who received 2 doses of BNT162b2 during lactation (VAX-L). VAX dyads had significantly higher serum anti-S IgG compared to INF dyads (p < .0001), while INF mothers had higher BM: serum anti-S IgA ratios compared to VAX mothers (p = .0001). Median IgG placental transfer ratios were significantly higher in VAX-P compared to INF mothers (p < 0.0001). There was a significant positive correlation between maternal and neonatal serum anti-S IgG after vaccination (r = 0.68, p = 0.013), but not infection. Conclusions: BNT161b2 vaccination in late pregnancy or lactation enhances systemic immunity through serum anti-S Ig, while SARS-CoV-2 infection induces mucosal over systemic immunity more efficiently through BM Ig production. Next generation vaccines boosting mucosal immunity could provide additional protection to the mother-infant dyad. Future studies should focus on identifying the optimal timing of primary and/or booster maternal vaccination for maximal benefit.