Maternal COVID-19 Vaccination, Infection Boosts Infant Antibody Response


Natural infection plus COVID-19 vaccination in pregnant mothers conferred more durable antibody responses in infants than natural infection alone.

In the general population, it has been documented that so-called hybrid immunity, from both natural infection with COVID-19 plus COVID-19 vaccination, confers more durable immunity. This is of particular interest in vulnerable populations that are ineligible for vaccination, notably newborns and infants less than 6 months old.

Data presented at IDWeek 2023, taking place October 11-14, in Boston, Massachusetts, demonstrated that natural infection alone in pregnant mothers does not confer durable immunity in their infants, suggesting that maternal vaccination may provide better protection to these infants in the months prior to their own vaccine eligibility.1

The study, presented by Sylvia M. LaCourse, MD, MPH, of the University of Washington, included 107 pregnant participants (mean age, 32 years) who had experienced COVID-19 infection during pregnancy. The status of anti-Spike (anti-S) IgG antibodies and neutralizing antibodies was evaluated through blood sample draws at various timepoints, including during pregnancy, at time of delivery or birth, at less than 3 months postpartum, and 3 to 6 months postpartum. Among the participants, 27% were asymptomatic, 71% had mild to moderate COVID-19 severity, and 2% experienced severe symptoms. Collectively, 2 participants were hospitalized and 7 received treatment related to COVID-19 infection. At time of delivery or birth, 35% of participants remained unvaccinated, 27% were vaccinated, and 35% had received a booster, with 3% having partial vaccination. Overall, 65% of participants had hybrid immunity (vaccination plus infection) at time of delivery or birth.

Key Takeaways

  • Hybrid Immunity Boosts Durable Response: Natural infection alone in pregnant mothers does not confer durable immunity to their infants, particularly in the months prior to their own vaccine eligibility.
  • Maternal Vaccination Benefits Infants: Infants born to unvaccinated mothers had lower levels of anti-S IgG+ antibodies and neutralizing antibodies at birth and during their first 6 months of life. In contrast, infants born to vaccinated mothers displayed higher antibody levels, suggesting that maternal vaccination can provide better protection to infants.
  • Efficient Transplacental Transfer: Pregnant individuals who were vaccinated during pregnancy appeared to have more efficient transplacental transfer of antibodies compared to those who had natural infection alone. This finding further supports the idea that hybrid immunity may offer greater protection to infants.

Blood tests revealed that unvaccinated mothers and their infants were less likely to have anti-S IgG+ antibodies (87% maternal, 86% infant cord blood) at birth versus those who were vaccinated (100% maternal and infant cord blood; all P ≤ .01). Results were similar for neutralizing antibodies (unvaccinated maternal: 86%, cord: 75% vs vaccinated maternal: 100% for all; all P ≤ .01). At less 3 to 6 months of age, the percent of infants delivered to unvaccinated months with anti-S IgG+ antibodies and neutralizing antibodies dropped to 50% and 14%, respectively, compared with infants delivered to mothers with hybrid immunity, who remained at 100% across both measures (all P <.01). Overall, infants born to unvaccinated mothers with anti-S IgG+ antibodies or neutralizing antibodies displayed lower median antibody levels at birth and through their first 6 months of life compared with infants born to vaccinated mothers.

Notably, those who were vaccinated during pregnancy appeared to have more efficient transplacental transfer of anti-S IgG+ antibodies and neutralizing antibodies versus natural infection alone (anti-S IgG+ antibodies: 97% vs 73%, P <.01; neutralizing antibodies: 86% vs 54%, P = .02), again suggesting that hybrid immunity may confer a greater level of protection to infants.

These findings are in line with conclusions from similar studies, including the MOMI-VAX study2 published in Vaccine earlier this year, which further demonstrated the advantage of a booster dose on antibody levels in both mothers and their cord blood. What's yet to be seen is more clear guidance on timing of vaccination/boosters that may confer the greatest amount of protection to mothers and their newborns.

Click here for more coverage of IDWeek 2023.

1. LaCourse SM, Wetzler EA, Aurelio MC, et al. Maternal hybrid immunity to SARS-CoV-2 during pregnancy provides more durable infant antibody responses compared to natural infection alone. Presented at: IDWeek 2023. October 11-14, 2023; Boston, MA. Abstract 2079.
2. Munoz FM, Posavad CM, Richardson BA, et al. COVID-19 booster vaccination during pregnancy enhances maternal binding and neutralizing antibody responses and transplacental antibody transfer to the newborn. Vaccine. 2023;41(36):5296-5303. doi:10.1016/j.vaccine.2023.06.032
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