COVID-19 Vaccine Safety in Pregnancy
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For the general adult population, the risk of severe COVID-19 illness is lower than it is for elderly individuals, the exception being pregnant and recently pregnant women, who have an elevated risk. There is a desire to protect people at higher risk, but none of the COVID-19 vaccine clinical trials included pregnant persons. There is also disinformation circulating that speculates that COVID-19 vaccines are associated with infertility, without providing any evidence for the claim. What do the scientific data say? What are the benefits and risks for pregnant persons when it comes to COVID-19 and the vaccines, and does the benefit of the vaccine outweigh the risk of infection?
Why were pregnant women excluded from COVID-19 vaccine trials?
The US Food and Drug Administration (FDA) placed an official ban on including women of “childbearing potential” in clinical research studies that lasted from 1977 until 1993.1 This was shortly after the medical field recognized that certain medications could cause serious birth defects if taken during pregnancy, the most notable example being thalidomide.
Ever since, the inclusion of pregnant women in clinical trials has been an ethically complicated issue since no one wants to run the risk of causing birth defects. However, there are still medical conditions that pregnant people face that warrant controlled studies to ensure medications are safe and effective. With a lifesaving COVID-19 vaccine available against a life-threatening virus, in the context of pregnancy, those who are expecting are having to make a complex decision. Thankfully, we have data to assist with that decision.
What do we know from the data we do have?
The Pfizer–BioNTech, Moderna, Oxford–AstraZeneca and Janssen vaccines have been evaluated in Developmental and Reproductive Toxicity (DART) studies.2,3,4,5 These studies involve administering high doses of the vaccine (several times higher than the human equivalent) in rodents or rabbits to analyze what happens in the animals and their offspring. The advantage here is that the animals have much shorter gestation periods (weeks) than humans (months) and they produce lots of offspring, meaning scientists have access to a large sample size for data collection. If there is an issue relating to safety, it will be easier to detect. In all the DART studies conducted for the COVID-19 vaccines to date, there has been no impact on the animal’s ability to get pregnant, stay pregnant or on pregnancy outcomes or birth defects either.
We have safety data in humans too, even though pregnant persons were not included in the original clinical trials. The US Centers for Disease Control and Prevention has been collecting data on people who self-identify as pregnant in their v-safe after vaccine health checker surveillance system and recently reported their findings for over 35,000 pregnant persons.6 When considering post-vaccination side effects, pregnant persons experienced the same kind of symptoms as non-pregnant persons. Surprisingly, pregnant women experienced these symptoms less frequently than their non-pregnant counterparts; the exceptions being pain at the injection site and fatigue. However, fatigue may be considered a side effect of pregnancy overall.
The CDC also looked at pregnancy outcomes among those who have been vaccinated for COVID-19. The frequency of pregnancy loss, pre-term birth, low birth weight and congenital anomalies was similar to the general population of pregnant women, therefore the mRNA vaccines appear to be safe for both mother and baby.
The adenovirus vaccine platform (featured in the Oxford–AstraZeneca and Janssen vaccines) has previously been tested in pregnant persons during clinical trials for HIV and Ebola vaccines with no significant safety concerns. 7 However, we should not ignore the elevated risk, especially for women of childbearing age, for cerebral venous sinus thrombosis (CVST) + thrombocytopenia that has been detected in recipients of the Oxford–AstraZeneca and Janssen vaccines. This rare but serious complication has not been associated with the mRNA vaccines (Pfizer–BioNTech or Moderna), and so these vaccines could be an attractive alternative for women of childbearing age.
Evidence also shows that the antibodies produced by the vaccinated mother transfer to their baby both through the placenta and through breastmilk after delivery.8,9 These antibodies confer temporary protection to their newborn. Of course, community efforts to keep case rates low through vaccination and non-pharmaceutical interventions (such as masking) will help to protect unvaccinated newborns also.
What is the risk of COVID-19 for pregnant persons?
Compared to uninfected pregnant women, those who are infected with SARS-CoV-2 while pregnant are five times more likely to be admitted to an ICU, six times more likely to be referred for high risk monitoring and 22 times more likely to experience maternal death. They are also more likely to require a cesarean delivery compared to a vaginal delivery.10 Findings such as these are part of the reason why the American College of Obstetricians and Gynecologists (ACOG) shared their own recommendations that vaccines be permitted for pregnant persons shortly after they were authorized in December 2020.11 Given the safety profile of the vaccines in pregnant persons to date, the benefits of vaccination appear to outweigh the risks, especially when compared to the risks associated with COVID-19 infection.
What about those who plan to become pregnant or who are lactating?
There is disinformation circulating that claims that the COVID-19 vaccines cause infertility, but after millions of people have been vaccinated to date, there are no data to support that claim. In fact, there is more reason to suspect that the COVID-19 infection may contribute to infertility, rather than the COVID-19 vaccines. For example, high fevers in men can reduce their sperm production; in COVID-19 disease, it is not uncommon to have several days of high fever.
According to the ACOG, “unfounded claims linking COVID-19 vaccines to infertility have been scientifically disproven.” It goes on to strongly encourage vaccination for non-pregnant individuals, including those who are trying to conceive and those who are lactating.
What about long-term effects of the vaccine?
Paul Offit is the director of the Vaccine Education Center at Children’s Hospital of Philadelphia. He recently said that the side effects associated with vaccines, if they are going to happen, have always appeared in the first two months after administration. He goes on to add, “There are no long-term effects where you find that one year [or] two years later your child or you develop some problem that wasn’t picked up initially. It has never happened.” Since December 2020, over 300 million vaccine doses of COVID-19 vaccines have been administered in the US alone. We are well past the two-month window. If there was going to be an unexpected side effect, we would have seen it by now – but we have not. Perhaps the most important long-term effect of vaccination is avoiding hospitalization and death from the disease, and isn’t that the goal, anyway?
Ultimately, the risks of COVID-19 infection are worse than any risk posed by COVID-19 vaccination for those who are pregnant, planning to become pregnant, or who are lactating. However, this can still be an anxious decision for many, and it is okay to have concerns. Your medical provider can be a valuable source of information and help you to weigh the risks and benefits if you are unsure.
1. Policy of inclusion of women in clinical trials. US Department of Health and Human Services. https://www.womenshealth.gov/30-achievements/04. Updated April 1, 2019. Accessed June 08, 2021.
2. Vaccines and Related Biological Products Advisory Committee December 10, 2020 Meeting Briefing Document: Pfizer-BioNTech COVID-19 Vaccine. US Food and Drug Administration. https://www.fda.gov/media/144245/download. Published December 10, 2020. Accessed June 08, 2021.
3. Vaccines and Related Biological Products Advisory Committee December 17, 2020 Meeting Briefing Document: Moderna COVID-19 Vaccine. US Food and Drug Administration. https://www.fda.gov/media/144434/download. Published December 17, 2020. Accessed June 8, 2021.
4. Assessment Report: COVID-19 Vaccine AstraZeneca. European Medicines Agency. https://www.ema.europa.eu/en/documents/assessment-report/vaxzevria-previously-covid-19-vaccine-astrazeneca-epar-public-assessment-report_en.pdf. Published January 29, 2021. Accessed June 8, 2021.
5. Bowman CJ, Bouressam M, Campion SN, et al. Lack of effects on female fertility and prenatal and postnatal offspring development in rats with BNT162b2, a mRNA-based COVID-19 vaccine. Reprod. Toxicol. 2021;103: 28-35. doi: 10.1016/j.reprotox.2021.05.007.
6. Shimabukuro TT, Kim SY, Myers, TR, et al. Preliminary findings of mRNA COVID-19 vaccine safety in pregnant persons. N Engl J Med. 2021. Online ahead of print. Last accessed June 8, 2021. doi: 10.1056/NEJMoa2104983.
7. Tapia MD, Sow SO, Ndiaye BP et al. Safety, reactogenicity, and immunogenicity of a chimpanzee adenovirus vectored Ebola vaccine in adults in Africa: a randomized, observer-blind, placebo-controlled, phase 2 trial. Lancet Infect Dis. 2020;20(6):707-718. doi: 10.1016/S1473-3099(20)30016-5.
8. Gray KJ, Bordt EA, Atyeo C, et al. Coronavirus disease 2019 vaccine response in pregnant and lactating women: a cohort study. Am J Obstet and Gynecol. 2021. doi: 10.1016/j.ajog.2021.03.023.
9. Perl SH, Uzan-Yulzari A, Klainer H, et al. SARS-CoV-2-Specific Antibodies in Breast Milk After COVID-19 Vaccination of Breastfeeding Women. JAMA. 2021;325(19):2013-2014. doi: 10.1001/jama.2021.5782.
10. Villar J, Ariff S, Gunier RB, et al. Maternal and neonatal morbidity and mortality among pregnant women with and without COVID-19 infection: The INTERCOVID Multinational Cohort Study. JAMA Pediatr. 2021. doi: 10.1001/jamapediatrics.2021.1050.
11. Vaccinating Pregnant and Lactating Patients Against COVID-19. The American College of Obstetricians and Gynecologists. https://www.acog.org/clinical/clinical-guidance/practice-advisory/articles/2020/12/vaccinating-pregnant-and-lactating-patients-against-covid-19. Updated April 28, 2021. Accessed June 08, 2021.
About the author
Amber Schmidtke, PhD, is a science communicator and medical educator who has previously worked at the Centers for Disease Control and Prevention and the Mercer University School of Medicine. You can follow her work here.