Babies born to mothers who were vaccinated against COVID-19 with an mRNA vaccine during pregnancy were less likely to test positive for SARS-CoV-2 in their first four months of life, according to a new study published in June 2022 in JAMA Internal Medicine.
Pregnant women are strongly encouraged to get the vaccine and the booster to reduce their own risk of severe COVID-19 symptoms, but researchers wanted to know if this benefit extends to newborns, as well. Children under 1 year of age are at higher risk of critical illness from COVID-19 compared to older children, according to a 2020 meta-analysis published in the Journal of Medical Virology.
It's known that maternal immunization against various illnesses, including pertussis and seasonal influenza, can provide passive protection to infants for the first few months after birth, due to antibodies passed through the placenta.
Researchers in Norway speculated the same is true for COVID-19 vaccination. They analyzed data on all live-born infants in the Medical Birth Registry of Norway from September 2021 through February 2022. In total, 21,643 infants were included in the study, 9,739 (45 percent) of whom were born to women who received a second or third dose of an mRNA vaccine during the last two trimesters of pregnancy.
The research indicated that infants born to vaccinated mothers had a lower incidence of SARS-CoV-2 during their first four months of life. During the Delta variant period (before Jan. 1, 2022), 0.5 percent of infants born to vaccinated mothers and 1.5 percent of infants born to unvaccinated mothers tested positive for COVID-19. During the Omicron variant period (starting Jan. 1, 2022), 4.0 percent of infants born to vaccinated mothers and 5.2 percent of infants born to unvaccinated mothers tested positive for COVID-19.
Research indicated that infants born to vaccinated mothers had a lower incidence of SARS-CoV-2 during their first four months of life.
The authors stated that of the 824 infants born to women who received a third vaccine dose during pregnancy, none had a positive SARS-CoV-2 test during the Delta wave. The risk of a positive test was also lower during the Omicron wave for women with a third dose compared to those with only two doses.
"We observed a lower risk of infection among infants born to women who received their third dose in pregnancy compared with the second, suggesting a stronger level of protection following the booster dose. This aligns with studies showing a waning of vaccine effect after the second dose unless a booster is received," the study authors stated.
In addition to the 21,643 infants included in the main analysis, the study authors reviewed the data of 2,839 infants who were born to mothers who received only one dose of mRNA vaccine during their second or third trimester. Of these, 36 infants tested positive for COVID-19 before 4 months of age. These results were not included in the main analysis.
"The findings of this study provide early evidence to suggest that infants benefit from passive protection from SARS-CoV-2 infection following maternal COVID-19 vaccination during pregnancy," the study authors concluded.