Maternal COVID-19 Vaccination Protects Against Infection in Early Infancy

In a study presented at IDWeek 2023 in Boston, Massachusetts, researchers found that receiving a maternal COVID-19 booster, particularly in the early third trimester, offered greater protection for infants younger than 6 months of age compared with infants of those who did not receive a maternal booster.

Although maternal vaccination for the prevention of COVID-19 in early infancy is widely considered a viable option, the amount of protection these vaccines provide to infants in the first 6 months of life is not well understood. Cardemil and colleagues aimed to quantify the amount of protection that SARS-CoV-2 antibodies provide to infants in the first 6 months of life.

For their study, researchers prospectively followed infants from birth up to 6 months at nine US academic sites born to mothers vaccinated during pregnancy with two doses (primary series alone) or three doses (primary series and a booster dose) of an mRNA COVID-19 vaccine.

At delivery, researchers measured anti-Spike IgG and pseudovirus neutralizing antibody (NAB) levels. They determined COVID-19 infection by verified maternal report between September 2021 and December 2022. The vaccine effectiveness between the two dose groups was estimated in separate models.

The results showed that maternal COVID-19 booster, particularly in the early third trimester, offered more protection for infants younger than 6 months of age compared with those who were not boosted. Indeed, when comparing infants in the boosted group (n = 181) vs the non-boosted group (n = 260) at delivery, researchers found that the boosted group had four times higher anti-Spike IgG at delivery vs the non-boosted group (mean 4443 vs 1091 BAU/ml; p < 0.001). Those in the boosted group also had three times higher pseudovirus NAB titers compared with the non-boosted group (1567 vs 404 IC50; p < 0.001). 

Additionally, researchers found that a 10-fold increase in anti-Spike IgG measured at delivery was associated with a 69.2% reduction in the infant’s risk of acquiring COVID-19 in the first 6 months (95% CI: 38.1%, 84.6%, p = 0.001). Having a pseudovirus NAB response above an IC50 of 20 at delivery was associated with a 96.2% reduction in the infant’s risk of getting COVID-19 in the first 6 months (95% CI: 75.1%, 99.4%; p = 0.001), according to Cardemil and colleagues.

In a separate model, researchers found that the relative vaccine effectiveness was 65% (95% CI: 24%, 84%) when accounting for changes in anti-Spike IgG levels and 83% (95% CI: 43%, 95%) when accounting for pseudovirus NAB levels.

“Higher SARS-CoV-2 IgG Spike and pseudovirus NAB titers at delivery are associated with a substantially reduced risk of COVID-19 infection for infants in the first 6 months of life,” the authors concluded. “Until infants are age-eligible for COVID-19 vaccination, maternal vaccination provides transplacentally transferred passive binding and neutralizing SARS-CoV-2 antibodies that protect against infection during early infancy.”

Reference
Cardemil CV, Cao Y, Posavad CM, Badell ML, Bunge K, Mulligan MJ, et al. Infant antibody titers at birth following maternal COVID-19 vaccination and protection against infection in the first 6 months of life. Talk presented at: IDWeek 2023. October 11-15, 2023. Accessed December 15, 2023. https://idweek.org/