Published: 06-02-2024 17:00 | Updated: 08-02-2024 13:00

Covid vaccine for pregnant women safe for newborn infants

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No increased risks for babies, and for some serious neonatal complications lower risks. This is the result of the largest study to date on the safety of newborn babies whose mothers were vaccinated against COVID-19 during pregnancy. The study is a collaboration between Swedish and Norwegian researchers and is published in the journal JAMA.

COVID-19 vaccination in pregnancy was not associated with any increased risks in newborn infants. On the contrary, the study of nearly 200,000 newborns in Sweden and Norway showed that babies born by women who chose to be vaccinated were less likely to suffer serious complications, including death. The mortality rate was only half as high in babies whose mothers had been vaccinated.

Portrait of Mikael Norman, dressed in black shirt and gray jacket, against a black background.
Mikael Norman. Photo: Stefan Zimmerman

“We made several attempts to explain this finding. A direct vaccine effect is unlikely. Previous studies have shown that the vaccine does not cross the placenta and that it cannot be found in umbilical cord blood," says Mikael Norman, professor of pediatrics and neonatology at the Department of Clinical Science, Intervention and Technology, Karolinska Institutet and first author of the study.

Instead, the researchers have adjusted for several background factors that were unevenly distributed in the two groups of women. They also conducted seven different subgroup analyses of women and newborns. 

“No matter how we look at it, the finding remains and therefore, we cannot say what the lower risk of death among infants of vaccinated women relates to," says Mikael Norman.

Registers in Sweden and Norway were used

The researchers used national registers in both countries and included 98 percent of all newborn babies of women who became pregnant after the vaccines became available. All births from gestational week 22 and onwards were included in the study. The first baby was born in June 2021 and the last one in January 2023. All babies were followed up for at least one month or as long as they were admitted to a neonatal unit.

In total, the study included 196 470 newborns where 48 percent of the mothers had been vaccinated with one or more doses of an mRNA vaccine against COVID-19. Almost 80 percent had received the Pfizer/Biontech vaccine and just over 20 percent the vaccine from Moderna.

In addition to lower infant mortality, the researchers also found a significantly lower risk of two other serious complications in infants born to mothers who had been vaccinated. In total, fifteen neonatal complications and conditions were studied. 

"We saw lower rates of cerebral hemorrhages and hypoxia-ischemic conditions of the brain in the newborns of vaccinated than in babies of unvaccinated in pregnancy, while the incidence of other bleedings, blood clots or inflammation in various organ systems did not differ between the groups," says Mikael Norman.

Important knowledge for the future

Despite the fact that the pandemic is over, 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, says Mikael Norman.

"COVID-19 is still present in society and is probably something we will have to deal with for a long time. It is therefore very important for the one hundred thousand women who become pregnant every year in Sweden, and the 130 million in the world, to know that vaccination with mRNA-vaccines against COVID-19 is safe for their babies. We found no increased risks, if anything, infants to vaccinated women had lower risks for some severe outcomes.”

The research was mainly funded by Region Stockholm and Karolinska Institutet, the Childhood Foundation of the Swedish Order of Freemasons, NordForsk, and the Norwegian Research Council. The researchers state that there are no conflicts of interest. 

Publication

"Neonatal Outcomes After COVID-19 Vaccination in Pregnancy" Mikael Norman, Maria C. Magnus, Jonas Söderling, Petur B. Juliusson, Lars Navér, Anne K. Örtqvist, Siri Håberg, Olof Stephansson. JAMA, online February 6, 2024, doi:10.1001/jama.2023.26945

Facts:

Pfizer's and Biontech's mRNA vaccine Comirnaty was approved on 21 December 2020, while Moderna's mRNA vaccine Spikevax was approved shortly after, on 6 January 2021. They were the first two Covid vaccines to be approved.

The two mRNA-vaccines were the only ones recommended for pregnant women in Sweden and Norway. Initially, vaccination was only recommended to pregnant women at high risk for COVID-19, but from May 2021 in Sweden and from August 2021 in Norway, general vaccination of pregnant women was recommended.

The complications affecting newborn infants of vaccinated mothers at significantly lower rates were rare, but they did occur in both groups.

Complication                      Vaccinated mothers           Unvaccinated mothers

Infant death                        0.9 out of 1,000 births        1.8 out of 1,000 births

Brain bleeding                    1.7 out of 1,000 births        3.2 out of 1,000 births

Brain hypoxia/ischemia      1.8 out of 1,000 births        2.7 out of 1,000 births

Sources: Fass, Läkemedelsverket and the study.