Studies continue to show that COVID-19 vaccines don’t harm fertility

Claims blaming COVID-19 vaccines for innumerable alleged harmful effects have been a constant throughout the pandemic. One persistent claim that spread even before a COVID-19 vaccine was available is that the vaccines cause infertility. This narrative has contributed to vaccine hesitancy, a stance with potentially harmful consequences.

On 20 September 2023, a Facebook video featuring gynecologist Christiane Northrup revived this old claim. The video received over 1,300 interactions and 1,400 shares.

Northrup’s video is a segment of a “Friday Roundtable” originally uploaded by the anti-vaccine organization Children’s Health Defense (CHD) in June 2022. This event revolved around a pseudo-documentary that had just been released titled “Infertility: A Diabolical Agenda”, produced by CHD founder Robert F. Kennedy Jr. and directed by former physician Andrew Wakefield, also present in the roundtable.

An article by the McGill Office for Science and Society referred to Wakefield’s film as an “Anti-Vaxx Sleight-of-Hand Propaganda”. Indeed, the central argument in the film is an old depopulation conspiracy theory claiming that vaccination campaigns aimed at eliminating maternal and neonatal tetanus in Kenya are just a cover-up for forcibly sterilizing women.

This claim, which dates back to the 1990s, is false and has been debunked thoroughly.

The film isn’t the first instance of Wakefield spreading misinformation about vaccines. He led a now-retracted study that incorrectly linked the measles, mumps, and rubella (MMR) vaccine to autism. The study was found to contain several critical flaws, including data fabrication and ethical violations. However, the belief that vaccines cause autism has persisted, even though many well-conducted studies published later showed no such association.

Apart from Northrup and Wakefield, the roundtable gathered several other personalities in the anti-vaccine community, including chemical engineer Brian Hooker, pediatrician Liz Mumper, and gynecologist James Thorp.

Northrup’s speech supposedly provided evidence that COVID-19 vaccines harm fertility, particularly in women. However, the data that Northrup cited doesn’t support her claim, as they don’t come from reliable scientific studies but from partial analyses with many critical flaws, as we will explain below.

Claim 1 (Flawed reasoning):

Raw data from a study published in the New England Journal “proves that 80% of the women who get the shot in the first and second trimester, basically zero to 20 weeks, have an 80% miscarriage rate. Now the miscarriage rate just baseline is one in six” 

This claim, which made the rounds online in July 2021, is based on a study published by the U.S. Centers for Disease Control and Prevention (CDC) in June 2021^[1]. In it, the authors evaluated the safety of the Pfizer-BioNTech COVID-19 vaccine in pregnant women using reports from the U.S. vaccine safety surveillance systems.

Northrup wasn’t the only one who has made this claim. In August 2023, another participant in the Friday Roundtable, Thorp, cited the same figure in a video interview with broadcast host Nicholas Veniamin.

But the 80% figure that Northrup and Thorp cited is based on flawed calculations that misrepresent the results of the study, as Health Feedback showed in an earlier review. Reuters, Full Fact, FactCheck.org, and PolitiFact, among others, also debunked the claim, pointing out the same flaws.

Briefly, the CDC analyzed data from 827 pregnant women who had received a COVID-19 vaccine and completed pregnancy—either with a positive or a negative outcome—before the study was released. Then, the authors calculated the rate of negative pregnancy outcomes, including miscarriage.

Among them, 104 (12.6%) experienced a miscarriage, a rate similar to that reported in other studies in pregnant women conducted before the pandemic. Therefore, the authors concluded that these results, although preliminary, didn’t suggest that the vaccine posed a risk to pregnant women.

However, some websites and social media posts argued that the authors should have calculated the miscarriage rate differently. Because miscarriage by definition can only occur in the first or second trimester, they asserted that all women who received the vaccine in the third trimester (700) should have been excluded from the calculation of the miscarriage rate, which would result in a miscarriage rate of 81.9% (104 out of 127).

But this calculation is incorrect and overrepresents miscarriages. When interpreting the study, it’s important to keep in mind that the study had been published somewhere between four to six months after the women included had been vaccinated. What this means is that most women who had been vaccinated in the first or second trimester could only have completed their pregnancy by the time of the study’s publication if they had miscarried or had an abortion.

Therefore, calculating the miscarriage rate in only women vaccinated during their first or second trimester with a completed pregnancy selects for a group in which miscarriage is the most likely outcome. And the minority who didn’t had an induced abortion instead, as the study’s data showed.

What would have been needed to calculate an accurate miscarriage rate was the pregnancy outcomes for all of the women vaccinated during their first and second trimester. However, the authors couldn’t obtain this information before the study was published, since many of these women’s pregnancies were still in progress.

Multiple robust studies conducted later show that COVID-19 vaccines aren’t associated with a higher risk of poor pregnancy outcomes, and don’t support the claim that COVID-19 vaccination jeopardizes pregnant women or their babies^[2-8]. On the contrary, by preventing severe illness, vaccination can actually reduce the risk of negative outcomes for both the mother and the baby^[9].

Claim 2 (Unsupported and Misleading):

“We had a group of about 20,000 women on Facebook who were talking about their experience with their menstrual cycle; they’d never seen anything like it. 90-year-olds beginning bleeding again. And we are not talking mild bleeding, we are talking clotting”

One of the central pieces of evidence in Northrup’s narrative that COVID-19 vaccines harm fertility is a project called My Cycle Story, which she conducted together with Thorp and Hooker, among others. According to the website, the project’s objective was to evaluate the effect of “exposure” to the spike protein on women’s reproductive health.

To do that, Northrup and colleagues distributed through social media a survey with 91 questions. A total of more than 6,000 women aged 18 years and above responded to the survey between 16 May 2021 and 31 December 2021. Then, based on the data collected, they conducted several analyses.

One of these analyses focused on the 3,390 unvaccinated women who hadn’t had a prior SARS-CoV-2 infection, and therefore, had “no prior exposure to the spike protein”. The website claimed that 85.5% of these women “had been in close proximity to someone who had been vaccinated” and that 71.7% of them reported irregular periods “Within a week of contact”.

Northrup and colleagues concluded that “proximity to vaccinated individuals increased the risk” of menstrual abnormalities, “suggesting a potential link” between these changes and COVID-19 vaccines. However, this conclusion is entirely based on the idea that people who received a COVID-19 vaccine can “pass” it to others, which is incorrect. As Health Feedback explained in an earlier review, there is no biological mechanism by which COVID-19 vaccines could cause shedding of either the virus or the spike protein.

Viral shedding is a phenomenon that can occur in live attenuated vaccines—like the vaccines against chickenpox—which use a live but weakened virus to induce immunity. People who receive this type of vaccine can produce and excrete vaccine-derived virus that may still retain the ability to replicate in cells. While these viruses are generally innocuous in healthy people, they might cause disease in some people like those with a weakened immune system.

However, none of the COVID-19 vaccines authorized in the U.S. and Europe use live virus. Most COVID-19 vaccines to date don’t even use the whole virus but only part of it, generally the spike protein. With regards to the mRNA COVID-19 vaccines specifically, they don’t contain the spike protein itself but rather the instructions that allow the cells to produce it. The mRNA and the spike protein have only a limited lifespan in the body and the small quantities in which they are produced haven’t been shown to cause harm.

In summary, the claim that unvaccinated women are experiencing changes in their menstrual cycles due to shedding from vaccinated people is baseless. Furthermore, the available evidence doesn’t suggest any safety concerns regarding menstrual cycles.

While the original clinical trials didn’t evaluate the effect of vaccination on menstrual cycles, several large studies since have addressed this question.

In January 2022, Edelman et al. published in Obstetrics & Gynecology the first study analyzing the effects of COVID-19 vaccines on menstruation in nearly 4,000 U.S. women aged 18 to 45^[10]. The study found that receiving one dose of a COVID-19 vaccine was associated with an increase in cycle length of less than one day compared to unvaccinated women.

The authors confirmed these results in a follow-up international study involving more than 19,000 women and published in the British Medical Journal in August 2022^[11].

It is important to note, however, that changes in cycle length of less than eight days are considered within the range of normal variability. Therefore, while the researchers did find a change, the small difference observed is very unlikely to have any clinical relevance.

The largest study published so far was conducted by researchers in Sweden and published in the British Medical Journal in May 2023^[12]. This study analyzed data from more than three million women and concluded that their findings “do not provide any substantial support for a causal association between covid-19 vaccination and healthcare contacts related to menstrual or bleeding disorders”, which directly contradicts Northrup’s claim.

Claim 3 (Unsupported and Misleading):

“269 women reported [decidual cast shedding]”; “It’s doing something to the coagulation pathways in the body. That is just the tip of the iceberg. I keep thinking when these young women realize they will never be able to get pregnant because they had that shot”

Again relying on the My Cycle Story survey, Northrup published a report focusing on decidual cast shedding (DCS), a rare gynecological event in which the lining of the uterus (endometrium) sheds in one large piece during menstruation. The report was published in the Gazette of Medical Sciences in April 2022. We couldn’t find this journal indexed in the scientific literature databases MEDLINE, PubMed Central (PMC), Web of Science, and Scopus.

Among all surveyed women, 292 (4.83%) reported having experienced DCS for the first time within the survey period, which the authors considered “unprecedented” compared to the baseline rate in the general population. The report also suggested that “exposure to the spike protein, either through natural exposure, vaccination, or shedding of the spike protein through exosomes” might be behind this and other menstrual abnormalities.

Northrup and colleagues then speculated that the alleged surge in DCS cases is due to coagulation problems caused by the COVID-19 vaccines.

But what Northrup didn’t say is that DCS isn’t usually a sign of a serious health problem. Although this event could be a sign of ectopic pregnancy in certain cases, especially when combined with other symptoms like sudden intense pain, this event alone generally isn’t associated with long-term medical problems or infertility, contrary to Northrup’s claim.

Furthermore, as we explained above, COVID-19 vaccines don’t cause shedding, and therefore can’t explain adverse events that occurred in unvaccinated people.

In addition, the report itself stated that literature about DCS is scarce, most of it consisting of case reports that “cannot determine a reliable prevalence of DCS events”.

Karen Duncan, an obstetrician and gynecologist at NYU Langone Health, told Bustle that decidual casts “are not commonly mentioned in OB-GYN textbooks and are mostly described in rare case studies in scientific literature”. The Cleveland Clinic also states that decidual casts are “rare” and “the exact number is unknown”.

Overall, this raises questions about how Northrup determined that the rate has increased, if there isn’t a reliable baseline estimate to compare current rates with.

Finally, the report itself stated that the survey “was not designed to determine the etiopathophysiology of this surge in DCS”. So, even if there were an increase, the report would be unable to establish its cause. Surveys can be very prone to biases, such as bias in the way participants are selected (selection bias) or a tendency for participants to retrieve information that confirms their own pre-existing ideas or beliefs (confirmation bias). These biases need to be minimized and corrected for^[13]. However, there is no indication that the authors tried to make such corrections in the report.

Claim 4 (Unsupported):

Fertility clinics have “never seen anything like it. The sperm of inoculated men does not swim. The eggs of inoculated women do not grow into embryos and those that do have a huge amount of contamination with stuff that’s non organic”

Northrup made this claim without providing any supporting data, only citing Carrie Madej as the source. Madej is an osteopath who spread the false claim that COVID-19 vaccines contain nano-technology living parasites. Health Feedback reviewed this claim in 2021, explaining that COVID-19 vaccines don’t contain living organisms of any kind, and there is no evidence that the organisms that Madej described even exist.

Likewise, the claim that COVID-19 vaccines impact men’s or women’s ability to conceive isn’t supported by any credible evidence. Studies on couples trying to conceive with^[14] and without fertility treatment^[15] showed no differences in the likelihood of conception between vaccinated and unvaccinated couples.

Several studies evaluated the potential impact of COVID-19 vaccines on sperm. One small study involving 37 men in Israel reported a temporary drop in sperm count after a second dose of the BioNTech-Pfizer COVID-19 vaccine^[16]. The authors attributed this effect to the fever that often occurs as a side effect of vaccination, and noted that the sperm wasn’t damaged and the counts returned to normal levels after a few months.

But other studies found no differences in the sperm’s volume, concentration, morphology and motility between vaccinated and unvaccinated men^[17-20].  In contrast, several studies have reported a decrease in sperm counts and quality following a SARS-CoV-2 infection^[21-23].

Conclusion

Claims that COVID-19 vaccines cause fertility and pregnancy problems are unsubstantiated and contradict the available evidence. Published studies so far show that COVID-19 vaccines are safe for pregnant women and not associated with pregnancy complications or infertility in men or women. It is COVID-19 itself that increases the risk of pregnancy complications and poses a risk to both the mother and the baby. Contrary to these claims, COVID-19 vaccination helps reduce the risk of harm to the mother and baby.

REFERENCES

• 1 – Shimabukuro et al. (2021) Preliminary Findings of mRNA Covid-19 Vaccine Safety in Pregnant Persons. New England Journal of Medicine.
• 2 – 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.
• 3 – Magnus et al. (2021) Covid-19 Vaccination during Pregnancy and First-Trimester Miscarriage. New England Journal of Medicine.
• 4 – Zauche et al. (2021) Receipt of mRNA Covid-19 Vaccines and Risk of Spontaneous Abortion. New England Journal of Medicine.
• 5 – Rimmer et al. (2023) The risk of miscarriage following COVID-19 vaccination: a systematic review and meta-analysis. Human Reproduction.
• 6 – Prasad et al. (2022) Systematic review and meta-analysis of the effectiveness and perinatal outcomes of COVID-19 vaccination in pregnancy. Nature Communications.
• 7 – Goldshtein et al. (2022) Association of BNT162b2 COVID-19 Vaccination During Pregnancy With Neonatal and Early Infant Outcomes. JAMA Pediatrics.
• 8 – Fell et al. (2022) Risk of preterm birth, small for gestational age at birth, and stillbirth after covid-19 vaccination during pregnancy: population based retrospective cohort study. BMJ.
• 9 – Halasa et al. (2022) Effectiveness of Maternal Vaccination with mRNA COVID-19 Vaccine During Pregnancy Against COVID-19–Associated Hospitalization in Infants Aged <6 Months — 17 States, July 2021–January 2022. Morbidity and Mortality Weekly Report.
• 10 – Edelman et al. (2022) Association Between Menstrual Cycle Length and Coronavirus Disease 2019 (COVID-19) Vaccination: A U.S. Cohort. Obstetrics and Gynecology.
• 11 – Edelman et al. (2022) Association between menstrual cycle length and covid-19 vaccination: global, retrospective cohort study of prospectively collected data. BMJ.
• 12 – Ljung et al. (2023) Association between SARS-CoV-2 vaccination and healthcare contacts for menstrual disturbance and bleeding in women before and after menopause: nationwide, register based cohort study. BMJ.
• 13 – Choi and Pak (2005) A Catalog of Biases in Questionnaires. Preventing Chronic Disease.
• 14 – Zhang et al. (2023) Effect of COVID-19 vaccination on the outcome of in vitro fertilization: A systematic review and meta-analysis. Frontiers in Public Health.
• 15 – Wesselin et al. (2022) A Prospective Cohort Study of COVID-19 Vaccination, SARS-CoV-2 Infection, and Fertility. American Journal of Epidemiology.
• 16 – Gat et al. (2022) Covid-19 vaccination BNT162b2 temporarily impairs semen concentration and total motile count among semen donors. Andrology.
• 17 – Barda et al. (2022) The impact of COVID-19 vaccine on sperm quality. International Journal of Gynecology and Obstetrics.
• 18 – Lifshitz et al. (2021) Does mRNA SARS-CoV-2 vaccine detrimentally affect male fertility, as reflected by semen analysis? Reproductive Biomedicine Online.
• 19 – Reschini et al. (2022) COVID-19 Vaccination Does Not Affect Reproductive Health Parameters in Men. Frontiers in Public Health.
• 20 – Gonzalez et al. (2021) Sperm Parameters Before and After COVID-19 mRNA Vaccination. JAMA.
• 21 – Depuydt et al. (2023) SARS-CoV-2 infection reduces quality of sperm parameters: prospective one year follow-up study in 93 patients. eBioMedicine.
• 22 – Martinez et al. (2023) COVID-19 associates with semen inflammation and sperm quality impairment that reverses in the short term after disease recovery. Frontiers in Physiology.
• 23 – Aksak et al. (2022) Investigation of the effect of COVID-19 on sperm count, motility, and morphology. Journal of Medical Virology.