In our last shocking news, a pregnant woman was infected with the Covid 19 virus which was transmitted to the foetus and led to complications such as delivering the baby prematurely. The findings from that news suggested an intensive research on monitoring pregnant women who have COVID, and consider them as a high risk group.

A group of researchers in Massachusetts studied pregnant women’s response to two approved mRNA vaccines – Pfizer/BioNTech and Moderna/NIH. The women were vaccinated either during pregnancy or while breastfeeding, and their ability to produce virus-specific antibodies was compared to that of vaccinated, non-pregnant women.

The Massachussets study focused on 84 pregnant women, 31 who were breast-feeding and 16 who were neither. The women each received two doses – what is known as prime and boost - of one of the vaccines. They had blood taken with each dose, and again up to six weeks after the second.
These blood samples were used to track the women’s antibody responses to the virus. The results were conclusive. All the women – both pregnant and breast-feeding – were found to have robust immunity, comparable to that of the non-pregnant women. And, this immunity increased with time, post-vaccination.

The researchers compared these findings with the antibody response in pregnant women who had contracted the virus naturally. This enabled them to show that the level of antibodies made in response to the vaccines far exceeded those made in response to natural infections.

One important reason to vaccinate pregnant women is so they can in turn provide their antibodies to the baby. This is known as passive immunity and it occurs when a mother is infected naturally or when she is vaccinated. The antibodies she produces are passed to her baby through the placenta or via breast milk. This affords the baby protection against infectious diseases it might come in contact with while its own immune system is still maturing.

When the babies in the study were delivered, the researchers studied blood samples from their umbilical cords. They found virus-specific antibodies in every sample. This shows that vaccinated mothers are passing antibodies to their babies through the placenta, in keeping with what we know from studies in natural infection. They also found virus-specific antibodies in breast milk from the women who were breastfeeding when vaccinated, which means that passive immunity is taking place via this route as well.

The investigators in this study were also able to provide some insight into when in pregnancy might be the best time to vaccinate pregnant women. Vaccinating women in different trimesters of their pregnancies did not affect antibody levels. This suggests that women can make a robust response to the vaccine at any stage of pregnancy.

In contrast, the analysis of umbilical cord blood shows that the second dose of a vaccine is important for maximising passive immunity for the baby. The lowest levels of antibodies in the umbilical cord samples came from a woman who delivered her baby before the second dose. The ability of the antibody to stop the entry of the virus into cells and cause infection also seems to need the boost dose. This suggests that having both doses before giving birth is critical to ensuring the baby gets the most protection possible.

There have been recent calls for pregnant women to be included at the early stages of vaccine trials, in order to limit delays in protecting them and their newborns.