Pfizer and Moderna are safe and effective in pregnant women, provide antibodies to newborns

Pregnant women were absent from the initial vaccine trials.

Pfizer and Moderna vaccines are safe and effective in pregnant and breastfeeding women, and these women can pass on protective antibodies to their newborns, according to a new study.

To reach that conclusion, the researchers studied a group of 131 women of reproductive age who received the Pfizer or Moderna vaccine, including 84 pregnant women, 31 breastfeeding women and 16 non-pregnant women, and found that antibody levels were similar in all three groups.

“This is very important information for our patients,” said Dr. Andrea Edlow, co-author of a study published Thursday in the American Journal of Obstetrics & Gynecology. “We know this vaccine works for you.”

Another common concern of pregnant patients is the side effects of the vaccine. The study did not find a significant difference in the side effects of the vaccine between pregnant women and non-pregnant study participants.

Compared with pregnant women who recovered from COVID, pregnant women who received the vaccine had “astonishingly higher” levels of antibodies. Interestingly, women who received the Modern version had higher levels of antibodies than those who received Pfizer. Antibodies generated by the vaccine were present in all umbilical cord and breast milk samples tested, suggesting that pregnant and lactating women transmit COVID-19 protection to their fetuses or newborns.

“It’s the most comforting information available,” said Galit Alter, study author and professor of medicine at the Ragon Institute.

The antibodies the researchers found in the mother’s blood were what is known as neutralization, meaning they have the ability to kill SARS-CoV-2 in laboratory tests, but more research needs to be done to determine if newborns have strong immunity after receiving vaccinated maternal antibodies. Future research could also help women decide when is the ideal time for pregnancy to get the vaccine for maximum protective benefits and determine if other vaccines, such as Johnson & Johnson and AstraZenec, work similarly to the two in the study.

The study had certain limitations. There were few, and the participants were mostly white health workers from one city. On the other hand, it is the largest study of the group that was left out of the initial vaccine trials. Absence of pregnant women from drug testing is a common practice for safety reasons, but in the case of COVID-19, the exclusion of many pregnant women has confused about whether it is safe to get vaccinated.

“They’re among the most vulnerable and weren’t involved,” Edlow said of the first vaccine trials.

According to the Centers for Disease Control and Prevention, pregnancy is considered a risk factor for serious COVID-19, including an increased risk of hospitalization and death from the virus. As of March 22, more than 80,500 pregnant women in the United States have been infected with the virus, and 88 have died, the CDC found.

Edlow, a specialist in maternal and fetal medicine from Massachusetts General Hospital, described an attempt to advise pregnant patients during a pandemic without data.

“We take care of patients on a daily basis who want to know if the vaccine is effective in pregnancy and what the risks are,” Edlow said. “Having real scientific data for counseling people goes a long way toward mitigating vaccine variability,” she added.

Both researchers hope that examples like their study encourage pharmaceutical companies to offer pregnant women the opportunity to participate in future vaccine studies, even outside of COVID-19.

“Otherwise this population sits at home contrite because they have no idea what to do,” Alter said.