Infants as old as 6 months were protected from COVID-19 infections only when mothers were vaccinated prenatally, and not before pregnancy, according to a new study in JAMA Network Open.
The study is one of the largest to compare outcomes among infants whose mothers were vaccinated before pregnancy, during pregnancy, or were unvaccinated at the time of birth.
Infants younger than 6 months are at an increased risk for severe COVID-19, and accounted for 44% of all pediatric COVID hospitalizations during the Omicron dominant period beginning in December 2021. Infants younger than 6 months remain the only group ineligible for COVID vaccination in the United States.
The present study was based on outcomes seen among all infants born to registered Singapore citizens and permanent residents between January 1, 2022, and September 30, 2022. Only infants whose parents had a confirmed case of COVID-19 during their first 6 months were included in the study.
"By selecting only infants with definite infant exposure to the virus due to the close contact between parents and newborn infants, we limited the possibility of the healthy vaccinee bias and overestimation of estimated vaccine effectiveness for infants," the authors explained.
VE for prenatal vaccination was 41.5% for second dose, booster
A total of 7,292 infants were included in the study, of whom 7,120 infants (97.6%) were born to mothers who had been fully vaccinated or boosted as of 14 days prior to delivery with mRNA vaccines. Of those, 39.5% were born to mothers who received their second dose during pregnancy, and 3,661 infants (50.2%) were born to mothers who received a third dose (booster) during pregnancy.
There may be a need for mRNA SARS-CoV-2 vaccination to be recommended for every pregnancy similar to maternal influenza and pertussis vaccination in order to maintain protection in newborns.
A total of 1,272 infants (17.4%) born to parents who were infected with SARS-CoV-2 postpartum also became infected during the study period, with a crude incidence rate of 174.3 per 100,000 person-days among infants born to unvaccinated mothers, 122.2 per 100,000 person-days among infants born to mothers vaccinated before pregnancy, and 128.5 per 100,000 person-days among infants born to mothers vaccinated during pregnancy.
The estimated vaccine efficacy (VE) was 15.4% (95% confidence interval [CI], -17.6% to 39.1%) for infants born to mothers vaccinated before pregnancy, and 41.5% (95% CI, 22.8% to 55.7%) among infants born to mothers vaccinated during pregnancy.
The VE increased to 44.4% (95% CI, 26.2% to 58.1%) if mothers received a third dose (booster), compared with 37.6% (95% CI, 17.2% to 53.1%) if mothers received their second dose, the authors said.
"There may be a need for mRNA SARS-CoV-2 vaccination to be recommended for every pregnancy similar to maternal influenza and pertussis vaccination in order to maintain protection in newborns," the authors said.