The administration of COVID-19 vaccines in pregnancy raises two kinds of concerns that apply to all vaccines. The first is the recognition that because the vaccines will be administered mainly to a healthy population, their safety must be well established. The second is whether there could be untoward effects on the developing fetus and cause adverse perinatal or post-natal outcomes.
The first concern was resolved both during the extensive clinical trials of the original COVID-19 mRNA and subunit vaccines and was subsequently confirmed when a large group of Canadian investigators found that maternal mRNA COVID-19 vaccination during pregnancy confers protection against infection by the SARS-CoV-2 virus (which causes COVID-19) and COVID-19–related hospital admission in newborns and young infants. Specifically, the authors reported in an article published in February 2023:
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.
These were important findings because pregnant women and their infants are considered to be at high risk for morbidity and mortality from viral infections. It has long been known that pregnant women who contract rubella ("German measles") are at risk for miscarriage or stillbirth and that their developing babies are at risk for severe birth defects with devastating, lifelong consequences. (The MMR vaccine protects against measles, mumps, and rubella.)
Another example is the disproportionate mortality and morbidity pregnant women have experienced during influenza pandemics. During the 1918 Spanish influenza pandemic, 50% of infected pregnant women died, and, despite advances in medical care and public health over the subsequent century, during the 2009 H1N1 influenza pandemic, infected pregnant women had a seven-fold higher need for intensive care compared with those who were not pregnant. They also accounted for 5% of H1N1 flu-associated deaths in the U.S., although they represented only 1% of the population and were skewed toward a younger demographic.
A more recent study of COVID vaccination by the same Canadian group that performed the one described above evaluated newborn and young infant safety outcomes following maternal vaccination with mRNA COVID-19 vaccines during pregnancy in a population-based, retrospective cohort study of live births in Canada. The investigators studied 142,006 single-offspring, live births, 60% of whom had been born to mothers who received one or more mRNA COVID-19 vaccine doses during pregnancy and compared them with the infants of unvaccinated women.
Here's the punchline:
The study found that the risks of severe neonatal morbidity, neonatal death, and admission to the neonatal intensive care unit were all significantly lower during the first month of birth in infants whose mothers had received at least one dose of a COVID-19 vaccine, and protection continued for six months after birth.
In an accompanying editorial, Catherine Mary Healy, MD, of Baylor College of Medicine in Houston, and Laura Riley, MD, of Weill Cornell Medicine in New York City, observed:
Safe and effective vaccines such as the COVID-19 vaccine should provide confidence in the maternal vaccination program where maternal vaccines provide protection for mothers and neonates against potentially devastating infections.
They also wrote:
Studies consistently demonstrate ... that the single most important factor in vaccination uptake in all populations is receiving a strong recommendation from a trusted health care professional, and for pregnant women, this patient-clinician relationship is particularly strong.
Those messages are important, given the deluge of anti-vaccine disinformation that is flooding the Internet these days and the fact that pregnant women are under-vaccinated compared to their non-pregnant counterparts. We need to get the word out that COVID vaccines protect pregnant women and their fetuses and infants.
Henry I. Miller, MS, MD, is the Glenn Swogger Distinguished Fellow at the American Council on Science and Health. He served for fifteen years at the US Food and Drug Administration (FDA) in a number of posts, including as the founding director of the Office of Biotechnology.