May 15, 2021

COVID-19 Vaccines Very Effective for Pregnant Women and Their Babies, New Study Finds


COVID-19 vaccines have been shown to be highly effective during pregnancy, according to a recent study published in the magazine American Journal of Obstetrics and Gynecology. The study has also shown that mothers who have been vaccinated transmit a prized immunity to their newborns.

A group of Massachusetts researchers studied the response of pregnant women to two vaccines, Pfizer / BioNTech and Moderna. The women were vaccinated during pregnancy or lactation, and their ability to produce specific antibodies against the virus was compared with that of vaccinated women who were not pregnant.

Although the small number of women included in this study (131) is a limiting factor, it provides very important early information on the safety and efficacy of vaccination during pregnancy. This is important because new infectious diseases can carry all kinds of risks for women during pregnancy and childbirth, as well as in the neonatal phase.

All of these risks must be taken into account when making health care decisions related to pregnant women and, in particular, when considering vaccination strategies.

Known risks

While much remains to be unraveled about the effects of COVID-19 on pregnant women and their babies, there are a few things we do know.

In early pregnancy, the virus not associated with an increased chance of miscarriage. Vertical transmission, in which the virus passes from the mother’s uterus to the baby, is relatively rare. And babies rarely get sick.

We also know that, in general, pregnant women tend to have milder symptoms than the general population. However, they remain at increased risk for complications, including placental inflammation, and can become seriously ill.

This, in turn, can lead to a greater chance of being admitted through intensive care services and giving birth prematurely. Similar to the general population, black or Asian pregnant women, as well as obese women, are at increased risk for severe COVID-19.

Now, of course, vaccination would prevent these results. However, women are generally not included in early vaccine trials if they are pregnant. Right now they are emerging data specifically related to the response to the vaccine of pregnant and lactating women. The work published in this article is the first study to address this topic, which makes it incredibly valuable.

Antibody response

The Massachusetts study focused on 84 pregnant women, 31 who were breastfeeding and 16 who were not. Each of the women received two doses, known as a prep and booster, of one of the vaccines. Blood was drawn with each dose, and again for 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 overwhelming. All women, both pregnant and lactating, were found to have strong immunity, comparable to non-pregnant women. And this immunity increased long after vaccination.

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

The Conversation

Passive immunity

An important reason to vaccinate pregnant women is that they, in turn, can provide their antibodies to the baby. This is known as passive immunity and occurs when a mother becomes infected naturally or when she is vaccinated. The antibodies it produces are passed on to your baby through the placenta or through breast milk.

This provides protection for the baby against infectious diseases that it may come in contact with while its own immune system is still maturing. It is one of the reasons, for example, that pregnant women in many countries are encouraged to get vaccinated against the flu and whooping cough.

When the study babies were born, the researchers studied blood samples from their umbilical cords. They found virus-specific antibodies in each sample. This indicates that vaccinated mothers are transmitting antibodies to their babies through the placenta, based on what we know from studies of natural infections.

They also found virus-specific antibodies in the breast milk of the women who were breastfeeding when they were vaccinated, meaning that passive immunity is also occurring through this route.

The researchers in this study were also able to provide information on what time of pregnancy is most suitable for vaccinating women. Vaccination of women in different trimesters of their pregnancy did not affect antibody levels. This suggests that women can have a robust response to the vaccine at any stage of pregnancy.

On the contrary, the analysis of the umbilical cord blood shows that the second dose of a vaccine is important to maximize the passive immunity of 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 virus from entering cells and causing infection also appears to require a booster dose. This suggests that taking both doses before giving birth is essential to ensure that the baby receives the best possible protection.

Next steps

Recently it has been requested that pregnant women are included in the early stages of vaccine trials to limit delays in protecting them and their newborns. This study supports those requests.

The study also highlights important next steps. Larger studies are needed to investigate when is the best time in pregnancy to vaccinate. These should include a more detailed discussion of how mothers respond to the vaccine at different stages of pregnancy, whether the vaccine prevents placental inflammation and preterm birth, and what effects this time might have on passive immunity in newborns.

It also addresses other relevant issues. How effective is the immunity transferred to the baby? And how long does the vaccine-induced viral immunity last in the mother when the vaccine is given during pregnancy? We will need more studies to answer these questions.

Catherine Thornton is Professor of Human Immunology at the University of Swansea (Wales) and April rees has a PhD in Immunology Research from Swansea University.

This article was originally published on The Conversation in English. You can read it here.

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