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• By Cara Murez HealthDay Reporter
• Posted June 30, 2022

What's the Best Timing for COVID Shots in Pregnancy?

Getting a COVID-19 vaccine during pregnancy can help protect both mother and baby.

But does it matter which vaccine or at what stage of pregnancy a woman receives her shots? New research suggests it does, and that getting immunized earlier in pregnancy may be better.

In their study, investigators focused on maternal immune responses to the vaccine and the transfer of COVID antibodies to the fetus through the placenta.

"Our goal was to compare maternal antibody responses and transplacental transfer of antibody to the neonate with vaccination across all three trimesters of pregnancy, and across different vaccine platforms [Moderna, Pfizer, and Johnson & Johnson]," said study co-senior author Dr. Andrea Edlow, a maternal-fetal medicine specialist at Massachusetts General Hospital and an assistant professor of Obstetrics, Gynecology, and Reproductive Biology at Harvard Medical School.

"We hope to use this information to better counsel patients wondering about vaccination in the first versus the second or third trimester," Edlow said in a hospital news release.

The researchers studied the antibody responses in 158 pregnant women who used Janssen's adenovirus-based vaccine, Moderna's mRNA vaccine and Pfizer's mRNA vaccine. They also evaluated maternal and umbilical cord blood in 175 maternal-neonatal pairs.

The team found lower-functioning antibodies in women who received the adenovirus-based vaccine than in those who received the mRNA vaccines. It also found subtle advantages in antibody levels and function in women who received the Moderna vaccine over the Pfizer vaccine.

The mRNA vaccine-induced antibodies had higher levels and functions against the Alpha, Beta, Delta and Gamma variants, as well as vaccine-induced antibodies with neutralizing activity against Omicron.

Getting vaccinated in the first or third trimesters lead to more maternal immune responses relative to second-trimester vaccination. However, the transfer of antibodies to the fetus through the placenta was most efficient with first and second trimester vaccination.

"These data support the initial vaccine series early in pregnancy if it has not yet been administered, with possible boosting later in pregnancy if eligible, to optimize protective antibody titers for both mother and neonate," said co-senior study author Galit Alter, a core member at the Ragon Institute of MGH, MIT and Harvard and a professor of medicine at Harvard Medical School.

The authors called for further research.

"Additional studies are needed to understand how to optimize maternal and neonatal immunity induced by vaccines in general during pregnancy," said co-senior study author Dr. Kathryn Gray, an associate obstetrician at Brigham and Women's Hospital in Boston and an assistant professor of obstetrics, gynecology, and reproductive biology at Harvard Medical School.

The findings were published in Nature Communications.

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