The small study, published in the American Journal of Obstetrics and Gynaecology, analysed the blood of 27 pregnant women who had received either the Pfizer or Moderna vaccine in their third trimester and the umbilical cord blood of their 28 newborns (26 singletons, one set of twins).AAfter receiving vaccination, women mounted a robust immune response suggesting that the vaccine will protect pregnant women from Covid-19, said the researchers from Northwestern Medicine in Illinois, US.

Additionally, in most patients, a longer period of time (latency) between vaccination and delivery was associated with a more effective transfer of Covid antibodies to the newborn baby.

Only three infants (including the set of twins) did not have positive antibodies at birth, and those two women had received their first vaccine less than three weeks prior to delivery.

Women who received the second dose of the vaccine before they delivered also showed an increased likelihood of transferring antibodies to their baby, the study found.

"This just gives extra fuel for people who are on the fence or just think, 'Maybe I'll wait until after I deliver'," said Emily Miller, Assistant Professor and physician at Northwestern University Feinberg School of Medicine.

"We strongly recommend you get the vaccine while pregnant. But if you're fearing vaccination might harm the baby, these data tell us quite the opposite. The vaccine is a mechanism to protect your baby, and the sooner you get it, the better," Miller said.

The study builds another published research that found similar findings in 10 umbilical cord samples.

Vaccinating women even earlier in their pregnancies (first or second trimester) may also lead to a higher efficiency of antibody transfer.

However, it is still too early to test how well or how long the passively transferred antibodies will continue to protect babies after delivery, Miller said.