Does the COVID-19 Vaccine Cause Infertility?

The claim that COVID-19 vaccines cause infertility has been one of the most persistent and widely shared pieces of vaccine misinformation since rollout began. It isn't supported by the evidence. Large studies, ongoing safety monitoring and professional medical bodies including the Royal College of Obstetricians and Gynaecologists (RCOG) have all reached the same conclusion: there's no evidence COVID-19 vaccines affect fertility in men or women.

Where the myth came from

The claim traces back to a document circulated online in late 2020 by a former Pfizer employee, which speculated that a spike protein component in some COVID-19 vaccines might be similar enough to a protein called syncytin-1, which plays a role in placental formation, that vaccine-induced antibodies could theoretically cross-react with it and affect fertility. This claim spread rapidly on social media, often alongside references to an entirely unrelated 1989 study on a fertility-focused vaccine that had nothing to do with COVID-19.

Scientists reviewed the underlying protein comparison directly and found the similarity between the two proteins was far too limited for the proposed mechanism to be biologically plausible. The RCOG has stated explicitly that there's no biologically plausible mechanism by which the current COVID-19 vaccines would affect fertility in women, directly addressing the theory the myth was built on.

What the actual research shows

Since the myth began circulating, a substantial amount of real-world data has been gathered specifically to test the claim and none of it supports it.

A large study funded by the US National Institutes of Health followed more than 2,000 couples trying to conceive and found no difference in the chances of conception whether either partner, or both, had been vaccinated, compared with unvaccinated couples. Separate research tracking IVF and ICSI fertility treatment cycles found inactivated COVID-19 vaccination did not affect treatment outcomes. Ongoing monitoring of large numbers of vaccinated women has continued to show normal rates of conception, miscarriage and healthy births, matching what would be expected without vaccination.

What about men specifically?

Multiple studies have measured sperm count, motility and shape before and after mRNA vaccination and found no significant changes attributable to the vaccine itself. This is a meaningful distinction from COVID-19 infection, which has been shown to cause temporary sperm quality changes; vaccination, without the illness, hasn't shown the same effect.

Does the vaccine affect miscarriage risk?

No. The UK's Human Fertilisation and Embryology Authority (HFEA) has stated there's no reason to postpone having a COVID-19 vaccine on the basis that it might affect miscarriage risk and vaccination doesn't increase that risk. This has been a specific area of monitoring precisely because early misinformation raised it as a concern.

Why the myth has been so persistent

Fertility is an emotionally significant topic and concerns about it tend to spread faster and stick around longer than more abstract worries, which likely explains why this particular myth has outlasted many other pieces of COVID-19 vaccine misinformation. It's also the kind of claim that's hard to disprove to someone's personal satisfaction with a single study, which is part of why health authorities have leaned on the cumulative weight of multiple large, independent studies rather than pointing to just one.

What official UK guidance says

The HFEA recommends that anyone having fertility treatment gets vaccinated, specifically because of the increased risks that COVID-19 infection itself poses during pregnancy, rather than because of any fertility concern about the vaccine. The British Fertility Society's guidance takes the same position, while noting it's reasonable to consider the timing of vaccination around a treatment cycle simply because some people experience short-term side effects like fatigue or a sore arm in the days afterwards, not because of any fertility-specific risk.

How this differs from genuine, acknowledged vaccine risks

It's worth being clear about the distinction between disproven myths and the rare, real risks that health authorities do openly acknowledge. A small increased risk of myocarditis, heart muscle inflammation, following mRNA vaccination has been identified, mostly in younger men and is actively monitored through the UK's Yellow Card reporting scheme. This kind of transparent, ongoing safety monitoring is exactly how a genuine risk like this one gets identified and communicated, which stands in contrast to the infertility claim, which hasn't been supported by any of the large studies specifically designed to test it.

This distinction matters because it shows the vaccine safety system is capable of catching and reporting real signals when they exist. If COVID-19 vaccines were genuinely affecting fertility at any meaningful scale, the same monitoring systems and large cohort studies that identified the rare myocarditis risk would be expected to pick up a comparable signal for fertility and to date, none have.

A quick recap

There's no credible evidence that COVID-19 vaccines cause infertility in men or women. The claim originated from a theoretical and since discredited, protein comparison and has since been directly tested by large studies covering conception rates, IVF outcomes, sperm parameters and miscarriage risk, none of which found a link. Bodies including the RCOG and HFEA continue to recommend vaccination for people trying to conceive or undergoing fertility treatment.

Frequently asked questions

Do I need to avoid the vaccine if I'm planning IVF?

No. The HFEA and British Fertility Society recommend vaccination for anyone undergoing fertility treatment, though you may wish to discuss timing with your clinic around side effects rather than fertility risk.

Does the vaccine affect the menstrual cycle?

Some people have reported temporary changes to their cycle after vaccination, similar to changes some experience after other vaccines or significant immune events, but current evidence doesn't show a lasting effect on fertility.

Is there any vaccine ingredient that could plausibly affect fertility?

No. Vaccine ingredients are publicly listed and independently reviewed and the specific biological mechanism the original myth relied on has been assessed as implausible by reviewing scientists.

Should men avoid the vaccine before trying to conceive?

No. Studies measuring sperm count, motility and shape before and after mRNA vaccination found no significant vaccine-related changes.

Why do so many people still believe this myth?

Fertility concerns tend to provoke strong emotional responses and spread widely on social media and the original claim was worded in a way that sounded scientifically plausible even though the underlying protein comparison didn't hold up under review.

Does this apply to all COVID-19 vaccines, not just mRNA ones?

The infertility studies conducted so far have covered several different vaccine types used internationally, including mRNA and inactivated vaccines and none have found a fertility effect, though mRNA vaccines have been the most extensively studied given how widely they were used in the UK.

Should I mention my vaccination history to a fertility specialist?

It's generally sensible to share your full vaccination and illness history with any fertility specialist, not because vaccination itself is a fertility risk factor, but because a complete health picture helps your clinician give you the most accurate advice for your situation.

Has the infertility myth affected vaccine uptake?

Surveys conducted during the pandemic found fertility-related concerns were among the most commonly cited reasons for vaccine hesitancy in people of reproductive age, which is part of why health authorities have continued to prioritise clear, direct communication addressing this specific claim, particularly when engaging with people planning a pregnancy.