Babies and Antibodies: How the COVID-19 Vaccine Affects Fetuses

By: Dynasti deGouville

On December 11, 2020, the Pfizer-BioNTech COVID-19 vaccine became the first of its kind available under the FDA’S emergency use authorization for those 16 years and older. Since then, 180 million Americans have gotten one or both doses of the Pfizer-BioNTech, Moderna, or Johnson & Johnson COVID-19 vaccine. Each company distributing the vaccines has emphasized the urgency of getting vaccinated as soon as possible if one is eligible. As of August 11, 2021, the vaccine is available to every individual 12 years of age and older unless they have other underlying health issues which exempts them from getting vaccinated. 

The COVID-19 vaccination, along with several other vaccinations, is recommended for those who are pregnant, breast feeding, trying to get pregnant now, or might become pregnant in the future. Evidence about the safety and effectiveness of COVID-19 vaccination during pregnancy has been growing.​​ This is extremely reassuring for pregnant and breastfeeding women who were left out of initial COVID-19 trials. These data suggest that the benefits of receiving a COVID-19 vaccine outweigh any known or potential risks of vaccination during pregnancy.[1]

According to the Centers for Disease Control and Prevention (CDC), pregnant people are more likely to become severely ill with COVID-19; they are also more likely to require hospitalization, intensive care, or ventilation, and may be at increased risk for adverse pregnancy outcomes. While some live vaccines such as the MMR vaccine, smallpox, or chickenpox vaccines should not be given to pregnant women because they may be harmful to the baby, the COVID-19 vaccine is a messenger RNA (mRNA) vaccine and runs no risk of causing disease in the person receiving the vaccine or their fetus. However, due to the nature of mRNA vaccines, researchers have been wondering how, if at all, immunity can be transferred from mother to infant. 

Studies have shown that a dynamic and adaptive immune system, not a suppressed system, is required for a successful pregnancy.[2] Pregnancy is an immunological balancing act in which the mother’s immune system has to tolerate paternal antigens and yet maintain normal immune competence for defense against microorganisms.[3] A study published in the American Journal of Obstetrics and Gynecology looked at 131 women of reproductive age with 84 pregnant women, 31 lactating women, and 16 non-pregnant women, all of whom have received either the Pfizer-BioNTech or Moderna vaccine.[4] Expectedly, the vaccine induced similar antibody levels and side effects across all three groups. In the largest study of its kind to date, researchers at Massachusetts General Hospital (MGH) found the COVID-19 mRNA vaccine to be highly effective at not only producing antibodies against the virus in pregnant and lactating women, but also in transferring antibodies to fetuses through the placenta, thus allowing the unborn child to build its own immunity against the virus. The presence of antibodies, which are proteins produced by the immune system to ward off future infections, in neonates suggests that immunity can be conferred from mother to child after maternal vaccination. 

Vaccine-generated antibodies were also present in all umbilical cord blood and breast milk samples. The umbilical cord acts as a link between the developing fetus and the placenta,  supplying the fetus with oxygenated, nutrient rich blood from the placenta. The presence of COVID-19 antibodies in the umbilical cord therefore provides clear evidence that the vaccine can induce immunity that will protect neonates. 

Another study published by the Journal of Obstetrics and Gynecology indicated that 99 percent of newborns had protective antibodies after their mothers received both vaccine doses, and 44 percent of babies had antibodies after one dose.[5] According to Weill Cornell Medicine, the researchers also found that vaccination led to antibody production in pregnant women as early as five days after the first dose, while the transfer of antibodies through the placenta to the baby occurred as early as 16 days after the first dose. The researchers also observed that the higher the maternal antibody levels, the higher the newborn antibody levels, and that the chances of having detectable antibodies in the mother and in their neonates increase with time elapsed since vaccination. 

Additionally, researchers have found that breastfeeding mothers can transfer COVID-19 antibodies to their infants soon after vaccination. This study found robust secretion of COVID-19 specific IgA and IgG antibodies in breast milk for 6 weeks after vaccination. IgA secretion was evident as early as 2 weeks after vaccination followed by a spike in IgG after 4 weeks (a week after the second vaccine). IgA antibodies are found in the linings of the respiratory tract and digestive system, as well as in saliva (spit), tears, and breast milk whereas IgG antibodies, the most common antibody, is found in blood.

Average levels of anti—COVID-19-specific IgA antibodies in the breast milk increased rapidly and were significantly elevated at 2 weeks after the first vaccine; average levels remained elevated for the duration of follow-up, and at week six, 65.7% of samples tested positive for COVID-19 antibodies.[6] This finding has been a breakthrough for breastfeeding women who were initially left out of COVID-19 vaccine trials and thus had minimal data to go off of when deciding to get vaccinated. 

While these studies have shown promising preliminary results, it is worth noting that the small sample sizes warrant further investigation. More studies are needed to determine how these antibodies transfer from mother to infant and why it does not happen in some cases. It is also necessary to determine whether or not these findings are generalizable, or able to be applied to the general public. 

The CDC recommends that all people over the age of 12 receive both doses of the vaccine. Despite pregnant and breastfeeding women being excluded from initial trials, the preliminary results show that it is beneficial for both mother and infant to get vaccinated. COVID-19 cases have increased substantially with the onset of the Delta variant, so it is more imperative now than ever to ensure that we are all protected. Pregnant and/or breastfeeding women who are not vaccinated, please check here to schedule your vaccine appointment for the health of you and your baby. 

Resources: 

[1] Gray, K., et al. (2021). Coronavirus disease 2019 vaccine response in pregnant and lactating 

women: a cohort study. American Journal of Obstetrics and Gynecology, 225(3), 

303.E1-303.E17. https://doi.org/10.1016/j.ajog.2021.03.023 

[2] Mor, G., Aldo, P., Alvero, A. (2017). The unique immunological and microbial aspects of 

pregnancy. Nature Reviews Immunology, 17, 469-482. 

https://doi.org/10.1038/nri.2017.64

[3] Weetman A. P. (1999). The immunology of pregnancy. Thyroid : official journal of the 

American Thyroid Association, 9(7), 643—646. 

https://doi.org/10.1089/thy.1999.9.643

[4] Gray, K., et al. (2021). Coronavirus disease 2019 vaccine response in pregnant and lactating 

women: a cohort study. American Journal of Obstetrics and Gynecology, 225(3), 

303.E1-303.E17. https://doi.org/10.1016/j.ajog.2021.03.023. 

[5] Prabhu, M., Murphy, E., Sukhu, A., et al. (2021). Antibody Response to Coronavirus Disease 

2019 (CODI-19) Messenger RNA Vaccination in Pregnant Women and Transplacental 

Passage Into Cord Blood. Journal of Obstetrics and Gynecology, 138(2), 278-280. 

doi:10.1097/AOG.0000000000004438

[6] Perl, S. H., Uzan-Yulzari, A., Klainer, H., et al. SARS-CoV-2-Specific Antibodies in Breast Milk 

After COVID-19 Vaccination of Breastfeeding Women. (2021). JAMA, 325(19), 

2013-2014. doi:10.1001/jama.2021.5782