A new study of almost 200,000 newborns in Sweden and Norway shows that maternal receipt of the COVID-19 vaccine during pregnancy poses no risk to infants, and instead prevents babies from suffering serious complications.

Moreover, the mortality rate for babies born to mothers who were vaccinated during pregnancy was half the rate of those whose mothers were unvaccinated. The study appeared yesterday in JAMA. The authors caution, however, that they were unable to explain why the mortality risk was so reduced among infants whose mothers were vaccinated.

“A direct vaccine effect is unlikely,” said Mikael Norman, PhD, first author of the study in a press release from the Karolinska Institutet in Stockholm, Sweden, where he practices. “Previous studies have shown that the vaccine does not cross the placenta and that it cannot be found in umbilical cord blood… 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.”