Covid vaccination during pregnancy helps protect infants from infection

Two doses of mRNA covid-19 vaccine during pregnancy show significant efficacy against delta and omicron infection in infants under six-months old. They also reduce hospital admission for covid-19 among the same subjects.

The findings appeared on Feb. 8, 2023 in the BMJ Today.

“In this study, we show that maternal covid-19 vaccination during pregnancy might have dual benefits by also conferring protection to their infants,” the authors said.

As background the authors added, “Covid vaccines are not yet licensed for infants under six months of age, but emerging evidence suggests that vaccination during pregnancy may reduce the risk of infection and hospital admission in infants as antibodies are transferred across the placenta and through breastmilk (a process known as passive immunity).”

The study involved infants younger than six months of age who were PCR tested for covid-19 infection between 7 May 2021 and 5 September 2022. This data was cross-referenced with each mother’s mRNA covid-19 vaccination history during pregnancy (one, two or three doses) or unvaccinated, and to records of delta and omicron-related hospitalizations of the infants.

The endpoint of the study was confirmed delta or omicron infection or hospital admission of the infants.

The investigators enrolled 8,809 infants, including 99 delta cases (4,365 controls) and 1,501 omicron cases (4,847 controls).

Vaccine effectiveness from two maternal doses was 95% against delta infection and 97% against infant hospital admission due to delta. Vaccine effectiveness was 45% (37% to 53%) against omicron infection and 53% (39% to 64%) against hospital admission due to omicron. Vaccine effectiveness for three doses was 73% against omicron infection and 80% against hospital admission due to omicron.

Vaccine effectiveness of two doses against infant omicron infection was highest when the second dose was administered in the third trimester (53%) compared with the first (47%) or second (37%) trimesters.

Vaccine effectiveness for two doses against infant omicron infection decreased from 57% between birth and eight weeks, and to 40% after 16 weeks of age.

The authors concluded, “Maternal covid-19 vaccination with a second dose during pregnancy was highly effective against delta and moderately effective against omicron infection and hospital admission in infants during the first six months of life. A third vaccine dose bolstered protection against omicron.”

In an accompanying editorial, Dana Danino MD of the Ben-Gurion University in Beer-Sheva, Israel and Ilan Youngster MD of the Sackler School of Medicine, Tel Aviv University in Tel Aviv, Israel added, “Although Jorgenson and colleagues’ study reinforces the value of maternal vaccination against covid-19 during pregnancy, more studies are needed to better inform vaccination recommendations in an evolving landscape of new SARS-CoV-2 strains and novel vaccines.”