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Newborns whose mothers received at least one mRNA COVID-19 vaccine during pregnancy had no worse outcomes than those whose mothers didn't get the vaccine during pregnancy, a large cohort study from Sweden and Norway found.

In fact, the unadjusted mortality rates for vaccine-exposed neonates in the two nations were about half of those for unexposed neonates, a difference that held up after adjustment for a variety of factors (adjusted odds ratio [aOR] 0.68, 95% CI 0.50-0.91), Mikael Norman, MD, PhD, from the Karolinska Institutet in Stockholm, and colleagues reported in .

Researchers found that neonates exposed to a maternal COVID-19 vaccine had lower odds for nontraumatic intracranial hemorrhage (aOR 0.78, 95% CI 0.61-0.99), and there was also a lower odds of hypoxic-ischemic encephalopathy with maternal vaccination in the second trimester (aOR 0.73, 95% CI 0.55-0.96).

Researchers adjusted for factors that included maternal age, BMI, education, country of birth, smoking status, season of conception, parity, multiple births, and gestational age. The findings were unaltered even after restricting the analyses to women without COVID-19 in pregnancy, infants born at term, infants without birth defects, and singleton births, Norman explained.

"We did not expect the lower risk for neonatal death to be so robust," Norman told 乌鸦传媒.

Notably, there were no cases of neonatal pericarditis, myocarditis, or other inflammatory neonatal diseases among infants after maternal vaccination during pregnancy, the authors pointed out.

"The study and the results are of great importance for healthcare professionals offering counseling, authorities issuing recommendations, and above all, for anyone who will become pregnant in the future," Norman said. "It is therefore very important for all women who become pregnant to know that vaccination with mRNA vaccines against COVID-19 is safe for their babies."

The current study provided more evidence that maternal mRNA COVID-19 vaccines are safe for newborns, Elizabeth Schlaudecker, MD, medical director of the division of infectious diseases at Cincinnati Children's Hospital, commented to 乌鸦传媒. "There was a period when we didn't really know 100% how [mRNA vaccines] would affect pregnant women," she said, because when the mRNA COVID-19 vaccines were being developed, trials excluded pregnant people. "We were recommending it [to pregnant people] but still gathering data at the time, which is not our favorite situation to be in."

The study's findings made sense, noted Schlaudecker. "We think that the mechanism of some of these injuries to infants when they're in utero is because Mom had an insult, like an infection," she explained. "We know, for example, that if a mom has influenza while she's pregnant, it leads to prematurity, low birth weight, and several other negative outcomes."

Schlaudecker was also impressed with the capabilities of Sweden and Norway to collect comprehensive vaccine data on all mothers and infants born in those countries. She noted that the U.S. failed to consistently track vaccination data over the course of the pandemic, making it difficult to study maternal vaccine outcomes in the U.S.

The population-based cohort study looked at data from all live births at 22 weeks or more of gestational age in Sweden and Norway between June 2021 and January 2023. Of the 196,470 newborn infants, 48% were exposed to at least one COVID-19 vaccination with an mRNA vaccine during pregnancy, with most being exposed to one or two vaccinations. Over half of neonates were male (51.3%) and most were born at term (93.8%). Of those exposed to a COVID-19 vaccine, about 80% were exposed to the Pfizer-BioNTech BNT162b2 (Comirnaty) vaccine and about 20% to the Moderna mRNA-1273 (Spikevax) vaccine. Overall, 32% of the infants were exposed during the first trimester, 43% during the second trimester, and 24% during the third trimester.

People vaccinated during pregnancy in both Sweden and Norway were older, of Nordic origin, had more education, more often nulliparous, and had more comorbidities than pregnant people who did not get vaccinated (P<0.001). Vaccine-exposed infants were less likely than infants with no exposure to the COVID-19 vaccine to be preterm, small for gestational age, or have decreased Apgar scores.

Researchers looked at a variety of possible negative outcomes among newborns including bleeding/thrombosis, inflammation/infection, central nervous system disorders, circulatory problems, problems with respiration, gastrointestinal problems, and neonatal mortality. They also examined a wide variety of covariates that may have influenced outcomes. All data were prospectively collected from national registers in Sweden and Norway.

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