Multiple studies show that COVID-19 vaccines don’t cause pregnancy or fertility problems, despite widespread claims on social media
Pregnant women are more likely to develop severe COVID-19 compared to non-pregnant women. COVID-19 also increases the risk of pregnancy complications, including preterm delivery and stillbirth. COVID-19 vaccines can prevent these risks and aren’t associated with any safety issues during pregnancy. Therefore, public health authorities recommend that pregnant women get a COVID-19 vaccine.
Factually inaccurate: Safety monitoring data and multiple studies show that COVID-19 vaccines don’t negatively affect conception, pregnancy, or male or female fertility. Current evidence indicates that COVID-19 vaccines don’t impair ovarian function nor cause the immune system to cross-react to the placental protein syncytin-1.
Inadequate support: Pfizer’s safety surveillance document contains adverse events reported following vaccination. These reports on their own are insufficient to demonstrate that the vaccine caused the adverse events or is unsafe.
Lack of context: COVID-19 vaccines might cause small changes in women’s menstrual cycles. However, these are within natural variation and don’t suggest any safety problems with the vaccine.
On 27 April 2022, The Epoch Times published an article in which gynecologist James Thorp and former Pfizer scientific advisor Michael Yeadon associated COVID-19 vaccines with poorer pregnancy outcomes and fertility problems. The article received more than 5,000 interactions on Facebook and Twitter, according to the social media analytics tool CrowdTangle.
Claims that COVID-19 vaccines reduce fertility, increase the risk of miscarriage, and cause menstrual changes aren’t new and likely contributed to COVID-19 vaccine hesitancy among pregnant women, who are at a higher risk of severe COVID-19 compared to non-pregnant women. A 2021 report from NewsGuard, an online tool that rates the credibility of news and information websites and tracks misinformation, listed such claims among the top COVID-19 vaccine myths spreading online.
As we explain below, these claims are unsubstantiated by scientific evidence. Data from safety monitoring and multiple studies show that COVID-19 vaccines don’t impair conception or fertility and don’t increase the risk of spontaneous abortion, stillbirth, preterm birth, low birth weight, and neonatal death[1-5]. In contrast, several studies indicate that developing COVID-19 during pregnancy increases the risk of preterm birth, stillbirth, and neonatal death[6-8]. Therefore, health authorities like the U.S. CDC recommend COVID-19 vaccination for people who want to conceive and are pregnant or breastfeeding.
This review analyzes the claims in The Epoch Times article in detail and explains why they are inaccurate and misleading.
Claim 1 (Inaccurate):
“[I]n responding to the synthetic piece of virus spike protein, women’s immune systems would also make an immune response to their own placental protein”
This claim originated from a 2020 open letter written by Yeadon and physician Wolfgang Wodarg and was debunked multiple times by Health Feedback and other fact-checking organizations. In brief, Yeadon and Wodarg claimed that the SARS-CoV-2 spike protein contains a sequence of amino acids—the building blocks of proteins—that is also present in syncytin-1, a human protein that has a crucial role in the correct formation of the placenta during pregnancy.
Based on this alleged similarity, Yeadon and Wodarg assumed that the immune response generated against the spike protein through COVID-19 vaccination would also target the body’s own placental protein and cause sterility due to a phenomenon called cross-reactivity.
However, the sequence that syncytin-1 and the SARS-CoV-2 spike protein have in common involves only four amino acids, which is too short to trigger a cross-reaction of the immune system, according to experts. Geneticists and immunologists found that this small sequence was also present in many other human proteins, some of them essential for the body’s function like actin, collagen, and hemoglobin. Cross-reaction against these proteins would have caused evident disorders in people who received the vaccine, something that wasn’t observed in clinical trials.
Akiko Iwasaki, a professor of immunology at Yale School of Medicine, went even further and disproved the claim experimentally, communicating the results in an opinion article for the New York Times in January 2021. If Wodarg and Yeadon’s claim were true, the antibodies generated against the SARS-CoV-2 spike protein through infection would also cross-react with syncytin-1. Iwasaki and another researcher, Alice Lu-Culligan, analyzed serum from women with COVID-19 and found no cross-reaction between the patient’s antibodies and syncytin-1. These results directly contradicted Yeadon’s claim.
A study published in October 2021 by researchers in Singapore arrived at the same conclusion. The authors examined plasma from 66 individuals collected before vaccination, 21 days after the first dose, and two months after the second dose, and found no cross-reactivity to syncytin-1 after vaccination.
In December 2021, Iwasaki’s group published a preprint—a manuscript that hasn’t undergone peer review—showing that COVID-19 vaccines didn’t cause fetal defects nor increased anti-syncytin-1 antibody blood levels in pregnant mice.
Another preprint published in May 2021 analyzed the levels of human syncytin-1 antibodies in the plasma and breast milk of ten pregnant and five breastfeeding women before and after receiving the Pfizer-BioNTech COVID-19 vaccine. While all women had high antibody levels against the SARS-CoV-2 spike protein four to seven weeks after vaccination, their antibody levels against syncytin-1 remained very low. Yeadon misrepresented a slight increase in syncytin-1 antibody signal after vaccination as evidence of “an immune response to their own placental protein”. However, the authors clarified that all the samples were well below the positive threshold for syncytin-1. They concluded:
“BNT162B2-vaccinated women did not transmit vaccine mRNA to breast milk, and did not produce a concurrent humoral response to syncytin-1, suggesting that cross-reactivity to syncytin-1 on the developing trophoblast, or other adverse effects in the breast-fed infant from vaccine mRNA ingestion, are unlikely.”
Claim 2 (Inaccurate and Misleading):
“The vast majority of those [lipid nanoparticles] are dispersed throughout the entire body”
“[T]he mRNA products (Pfizer & Moderna) would accumulate in ovaries”
These claims are based on a misinterpretation of biodistribution data submitted by Pfizer to Japan’s regulator Pharmaceuticals and Medical Devices Agency (PMDA). The researchers injected rats with lipid nanoparticles identical to the ones that enclose the mRNA in the COVID-19 vaccine. The lipid nanoparticles used in the biodistribution study carried a radioactive label. By measuring the level of radioactivity, the researchers could estimate how much nanoparticles entered in each tissue and how long it takes for the body to eliminate them.
As Health Feedback explained in an earlier review, pages 5 and 6 of the technical document submitted by Pfizer show that the largest concentration of lipid nanoparticles remained at the injection site (52.6% of the administered dose at one hour post-injection), followed by the liver (18.1% at eight hours post-injection). The amount present in the rest of the tissues didn’t exceed 1% of the administered dose, and was below 0.1% in most of them. Therefore, Thorp’s claim that “the vast majority” of the lipid nanoparticles disperse throughout the body is inaccurate.
Likewise, the peak concentration in the ovaries was very low (0.095% at 48 hours post-injection) as Abraham Al-Ahmad, an associate professor in pharmacology at Texas Tech University, pointed out in a blog post. This concentration might be even lower in human ovaries, because the dose of lipid nanoparticles in the COVID-19 vaccine is far lower than that used in the biodistribution study in rats. In an article on the blog Science-Based Medicine, David Gorski, a professor of surgery at Wayne State University estimated that the dose used in rats would be equivalent to about 18 to 35 times the dose used in humans.
There is also no evidence indicating that these small concentrations of lipid nanoparticles have any negative impact on ovarian function in rats, let alone in humans. In fact, a small study involving 32 women and published in Human Reproduction found that neither SARS-CoV-2 infection nor vaccination with the Pfizer-BioNTech COVID-19 vaccine impaired ovarian function in humans.
Claim 3 (Misleading):
“Women are having bleedings. The doctors in our area are doing hysterectomies in young women, like 30-somethings, they said, ‘Oh, it’s not unusual.’ Let me tell you, as a board-certified gynecologist, that’s very unusual. Women’s periods are messed up all over the place”
In an attempt to further support the false narrative that COVID-19 vaccines impact ovarian function, The Epoch Times article quoted gynecologist Christiane Northrup. Northrup has previously spread medical misinformation and was among the six great spreaders of the 2020 conspiracy theory video “Plandemic”, which propagated unsupported and inaccurate information about the COVID-19 pandemic, according to the New York Times.
Northrup didn’t provide any evidence supporting the claim that vaccinated women undergo hysterectomy more frequently than unvaccinated women. Hysterectomy is a surgical procedure to remove the uterus that is used to treat gynecologic problems such as cancers, endometriosis, and heavy bleeding. However, COVID-19 vaccines haven’t been associated with any of these conditions.
In 2021, many women reported changes in the menstrual cycles after receiving the COVID-19 vaccine, including longer, heavier, or more painful bleeding. But clinical trials generally don’t study this subject, and data about the effect of COVID-19 vaccines on women’s menstrual cycles were very scarce.
The first study evaluating the effect of COVID-19 vaccines on menstruation was published in Obstetrics and Gynecology in January 2022. The authors found no difference in the duration of the bleeding before and after vaccination in almost 4,000 women. They did find an increase of one day in the menstrual cycle length after vaccination. However, such change is within the range expected from natural variations in menstrual cycles, and the authors concluded that it doesn’t have any clinical implications.
Claim 4 (Misleading):
“Among the adverse events, particularly alarming are the ones that affected pregnant women. The documents say that there were 274 pregnancy adverse events, of which 75, or 27 percent were ‘serious.’”
The Epoch Times article referred to a safety surveillance report from the first three months post-authorization of the Pfizer-BioNTech COVID-19 vaccine, including data from 270 pregnant women. This document was part of the Biological License Application and was confidential until the U.S. Food and Drug Administration released it on 1 March 2022 in response to a Freedom of Information Act request.
Since its release, Pfizer’s document has been misused to promote the narrative that COVID-19 vaccines are unsafe and associated with multiple medical conditions, as this earlier Health Feedback review documented. However, the document contains information about adverse event reports, which on their own are insufficient to determine whether a vaccine is unsafe, as Health Feedback explained in this Insight article.
An adverse event is any health problem that occurred after vaccination, regardless of whether the vaccine caused it. This is different from a vaccine side effect, which has been established to be caused by the vaccine; one example is an allergic reaction to a vaccine ingredient. In other words, adverse event reports contain information about medical events that occurred after vaccination but on their own they cannot establish whether the event was caused by the vaccine.
In addition, adverse event reports might not be representative of the situation in the general population due to different types of limitations. For example, page 6 of the Pfizer’s document suggests that the number of serious adverse events might be overrepresented as compared to mild adverse events due to limitations in data processing:
“Due to the large numbers of spontaneous adverse event reports received for the product, the MAH [marketing authorizations holder] has prioritised the processing of serious cases, in order to meet expedited regulatory reporting timelines and ensure these reports are available for signal detection and evaluation activity […] Non-serious cases are processed as soon as possible and no later than 90 days from receipt.”
Given all these limitations, claims that the COVID-19 vaccine is unsafe for pregnant women or for the general population based on this document are misleading and unsupported.
Misinformation linking COVID-19 vaccines with pregnancy and fertility problems has been pervasive throughout the pandemic. However, such claims have no fundamental basis in scientific evidence. Current evidence from research studies and vaccine safety surveillance shows that COVID-19 vaccines don’t impair fertility and are safe during pregnancy. COVID-19 vaccines are effective at preventing severe illness, and are particularly important for pregnant women, who are more likely to develop severe COVID-19 compared to non-pregnant women. COVID-19 also increases the risk of pregnancy complications compared to pregnant women without COVID-19. This means that getting vaccinated would reduce the risk of poor outcomes during pregnancy, not increase it.
- 1 – Lipkind et al. (2022) Receipt of COVID-19 Vaccine During Pregnancy and Preterm or Small-for-Gestational-Age at Birth — Eight Integrated Health Care Organizations, United States, December 15, 2020–July 22, 2021. Morbidity and Mortality Weekly Report.
- 2 – Shimabukuro et al. (2021) Preliminary Findings of mRNA Covid-19 Vaccine Safety in Pregnant Persons. New England Journal of Medicine.
- 3 – Zauche et al. (2021) Receipt of mRNA Covid-19 Vaccines and Risk of Spontaneous Abortion. New England Journal of Medicine.
- 4 – Kharbanda et al. (2021) Spontaneous Abortion Following COVID-19 Vaccination During Pregnancy. JAMA.
- 5 – Magnus et al. (2021) Covid-19 Vaccination during Pregnancy and First-Trimester Miscarriage. New England Journal of Medicine.
- 6 – Stock et al. (2022) SARS-CoV-2 infection and COVID-19 vaccination rates in pregnant women in Scotland. Nature Medicine.
- 7 – Villar et al. (2021) Maternal and Neonatal Morbidity and Mortality Among Pregnant Women With and Without COVID-19 Infection: The INTERCOVID Multinational Cohort Study. JAMA Pediatrics.
- 8 – DeSisto et al. (2021) Risk for Stillbirth Among Women With and Without COVID-19 at Delivery Hospitalization — United States, March 2020–September 2021. Morbidity and Mortality Weekly Report.
- 9 – Prasad et al. (2021) No crossreactivity of anti-SARS-CoV-2 spike protein antibodies with Syncytin-1. Cellular and Molecular Immunology.
- 10 – Lu-Culligan et al. (2021) No evidence of fetal defects or anti-syncytin-1 antibody induction following COVID-19 mRNA vaccination. BioRxiv. [Note: This is a preprint that has not yet been peer-reviewed at the time of this review’s publication.]
- 11 – Mattar et al. (2021) Addressing anti-syncytin antibody levels, and fertility and breastfeeding concerns, following BNT162B2 COVID-19 mRNA vaccination. MedRxiv. [Note: This is a preprint that has not yet been peer-reviewed at the time of this review’s publication.]
- 12 – Bentov et al. (2021) Ovarian follicular function is not altered by SARS–CoV-2 infection or BNT162b2 mRNA COVID-19 vaccination. Human Reproduction.
- 13 – Edelman et al. (2022) Association Between Menstrual Cycle Length and Coronavirus Disease 2019 (COVID-19) Vaccination. Obstetrics and Gynecology.