Maternal Covid-19 vaccination offers infants immunity for up to 6 months

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 were vaccinated against Covid-19, and protection against the virus continued for up to six months after birth, according to a new study published Monday in JAMA Pediatrics.

“We hypothesized that this might be because we know that severe Covid in pregnancy is associated with pregnancy complications and so by protecting the mom, you would expect that perhaps incidence would be at a lower risk for some of those severe outcomes,” said Sarah Jorgensen, a researcher and pharmacist at the Institute of Medical Science at the University of Toronto and the first author on the study.

Jorgensen, who researches vaccines in pregnancy, added that it could also be because pregnant people who get vaccinated tend to have other characteristics that are related to better outcomes in infants, like coming from areas with higher levels of education and better socioeconomic factors.

This population-based cohort study observed 142,006 infants up to 6 months of age born to mothers who were either vaccinated or not during the first, second, or third trimester. Of those, 85,670 infants were exposed to one or more Covid-19 vaccine doses while in utero. Of note is that in this study, 60% of pregnant people were vaccinated. As a result, the researchers found that after one month, exposed infants were 14% less likely to experience severe neonatal morbidity, and they were also 53% less likely to die and 14% less likely to be admitted to the NICU.

This study adds to the body of research which shows that maternal vaccination, like with influenza, tetanus, diphtheria, and acellular pertussis (Tdap), and most recently RSV, leads to positive outcomes for mother and baby, according to an accompanying editorial.

“It looks like more good news about the safety of Covid-19 vaccines,” said Sonja Rasmussen, a pediatrician and professor of genetic medicine at Johns Hopkins School of Medicine. “Now we have really strong data in a big study including a lot of women in the first trimester of pregnancy that shows that this vaccine is safe.”

However, even though the data shows a positive trend in Ontario, Rasmussen, who was not a part of the study, explained that this might not be the case in the U.S. because of hesitancy and fears that the vaccine could cause birth defects, preterm labor, or spontaneous abortion. According to the editorial, based on the results of this study and similar ones before it, these fears are unfounded. Still, the Centers for Disease Control and Prevention found that in April 2022, about 50% of pregnant women were vaccinated either before or during pregnancy and that number dropped to 46% in October 2022.

“We need to continue to make sure that pregnant persons understand that this is a way that they can protect themselves, they can protect their babies from getting Covid-19 in the first few months of life, and that this is safe,” said Rasmussen, who is also an expert on infections in pregnancy.

According to the editorial, the best way to encourage pregnant people to get vaccinated is for clinicians to have a strong relationship with their patients, because having a strong recommendation in combination with access to vaccines makes it more likely that a mother will get vaccinated.

“People, I think, are reassured when they see these safety data. Physicians are reassured and I’m hoping that patients will be reassured too and recognize the importance of protecting their baby by getting the Covid-19 vaccine,” Rasmussen said.

Among the study’s limitations, Jorgensen and her colleagues pointed out that they could not adjust for things that weren’t in the databases, such as body mass index, tobacco use, use of other medications, or breastfeeding, which could have had an impact on the study findings.

“We did adjust for a lot of things, but there were some things that just weren’t available in our study,” Jorgensen said.

In the future, Jorgensen’s team will look at these infants and children as they get older and look back when they turn 2 years old.

“We’ll continue to do research on different outcomes, as well as following these kids as they get older,” Jorgensen said. “So far, the evidence has been reassuring both from our group here in Ontario as well as abroad.”