COVID-19, the vaccine, fertility and periods – your questions answered

by Dr Fran Yarlett · June 21, 2021

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Reviewed by Dr Melanie Davis-Hall on June 22, 2021

Covid-19 Coronavirus Vaccine
As younger people start booking in for their COVID-19 vaccinations, we’ve noticed many of you have concerns about periods and fertility (...those things which affect young women a lot!). We’re also aware that many “theories” are being bandied around the internet and social media. Here are the facts to answer your burning questions.

What’s the lowdown?

Shortened summary of the covid 19 vaccine and fertility and periods
Shortened summary of the covid 19 vaccine and fertility and periods

Read on to discover more about the facts and research currently being done on the COVID-19 vaccine and fertility, as well as the COVID-19 vaccine and periods … and to hear some of our user’s own experiences!

COVID-19 vaccine and fertility

Does the COVID-19 vaccine affect fertility?

The answer to this question from the experts is a resounding no. 

The President of the Royal College of Obstetricians and Gynaecologists, Edward Morris, says “there’s absolutely no scientific evidence to suggest that any of the COVID-19 vaccines affects fertility, for men or women, or any plausible biological reason that it would”. 

Most young women of childbearing age will have had 23 vaccinations by the age of 20 and there is no effect on fertility, so why should the COVID-19 vaccines be different?

Where did the rumour come from?

Early conspiracy theories circulated online suggested that the COVID-19 vaccine could disrupt the formation of the placenta and therefore affect fertility. A research group has addressed this rumour and its potential origins. 

We know the COVID-19 vaccines target the “spike protein” found on the outside of the COVID-19 virus. By neutralising this spike protein, the virus is unable to enter our cells to replicate and cause further infection.

The anti-vaxxer community claims there is an alleged similarity between the spike protein and a protein called syncytin-1 that embryos need to form a placenta. Their concerns are that this similarity causes the body to form an immune response against the placenta as well as the COVID-19 spike proteins.

The diagram below shows the amino-acid sequence (which is basically a map) of each protein, these have been taken from the original study paper itself (doi:10.3390/biology10030238). The similarity between them is highlighted in yellow.

1. Human Syncytin-1 Protein


2. COVID-19 Spike Protein COVID-19 Spike Protein

Covid Spike Protein
Kloc M, Uosef A, Kubiak JZ, Ghobrial RM. Exaptation of Retroviral Syncytin for Development of Syncytialized Placenta, Its Limited Homology to the SARS-CoV-2 Spike Protein and Arguments against Disturbing Narrative in the Context of COVID-19 Vaccination. Biology (Basel). 2021;10(3):238. Published 2021 Mar 19. doi:10.3390/biology10030238

As you can see……there really isn’t much similarity. It is likely that multiple proteins in the body would have this small identical sequence to the COVID-19 vaccine and there is no evidence of an immune response against other proteins. And now there is actual science completely disproving this theory (doi:

What research has been conducted to date?

Research groups have started where they usually do, in rats. 

In one lab study, female rats were injected with the full adult dose of the Pfizer COVID-19 vaccine three weeks before being introduced to some lovely male rats. 95% of the rats fell pregnant after, quite amazingly, three days. 

This is encouraging as animal and rat studies are considered the best tools available to predict potential problems in humans. It is difficult to design clinical trials looking at fertility in humans. 

It is rather unethical to force human women to get pregnant after their vaccinations. So instead, we have to look at data in real time as it happens, which thankfully NHS England have provided us with.

Dr Vicki Male, reproductive immunologist at Imperial College London reported to NHS England that “In the clinical trials, participants were asked to use reliable contraception, but nevertheless, 57 of them became pregnant by accident. These pregnancies occurred equally in the vaccinated, and the unvaccinated groups, telling us that being vaccinated doesn’t reduce your chances of getting pregnant”. These women were all meant to be using reliable contraception but obviously hadn’t found The Lowdown yet… 

Dr Male adds “In the US, at the end of March, 4804 post-vaccination pregnancies have been reported to the CDC although this is going to be an underestimate of the global total, because this is only Americans”. 

In men, studies have looked at the quality of sperm before and after vaccination with the Pfizer vaccine, and vaccination makes no difference to the quality of your sperm. However, infection with COVID-19 can have a negative effect on this. 

Finally, the COVID-19 vaccines are not known to cause any harm to, or affect the success of fertility treatments. Equal numbers of pregnancies have been counted in IVF cycles in both vaccinated and unvaccinated couples. 

Not only is there no scientific evidence linking the COVID-19 vaccines with fertility problems, the research so far is very reassuring and provides evidence to the contrary.

What do I do if I have concerns about the vaccine and fertility?

We advise you to avoid reading stories on social media that don’t have scientific references to support their claims. 

We would suggest searching for information from reliable sources including the Royal College of Obstetrics and Gynaecologists, the Royal College of Midwives, or the Centre for Disease Control and Prevention in the USA. 

If you feel you need to speak to a healthcare professional about fertility concerns, speak to your GP or one of The Lowdown women’s health team.  Remember that most couples don’t get pregnant in the first month of trying to conceive, but 85% of couples do within a year.

Talk to one of our friendly doctors

COVID-19 infection and periods

Does having COVID impact your periods?

Many women have been reporting changes to their periods following infection with COVID-19. This is of course only women who knew they had COVID-19, as one third of women still have absolutely no symptoms despite being infected and may therefore not get tested. 

One Lowdown user reports:

“Covid has completely changed my period. From how long it lasts, to the intensity of my cramps (mine have lessened thankfully), to the colour. Some months I’m 3-5 days early, others I’m 3-5 days late, occasionally on time. I thought as I continued to improve in my other long-hauler symptoms, this would balance out as well, but it has not. It’s almost as if I’m starting my period for the first time all over again.”

Menstrual irregularities in 237 women (of child bearing age) who had confirmed COVID-19 have been investigated by scientists in China. 20% of these women reported lighter periods, while 5% experienced heavier periods. One fifth of women experienced longer cycles, and this occurred in women with both mild or severe COVID-19 infection.

On follow up, 99% of the women’s menstrual changes had returned to normal within 2 months, so any changes are likely to be short lived. One 44 year old woman didn’t have a period for 4 months after COVID-19, but we don’t yet know whether age will have an impact on these changes. The length between periods also changes in the perimenopause (the time around and leading up to the menopause).

It is really important to remember that changes in the menstrual cycle are common after any severe illness and are related to the stress the body is under. However, clearly more research is needed to understand the true effects of COVID-19 on our periods.

COVID-19 vaccine and periods

Does having the COVID-19 vaccine impact your periods?

No previous vaccination has had as much media interest as the COVID-19 vaccines. Side effects and adverse reactions are identified by patients and healthcare professionals who report them via the MHRA’s Yellow Card scheme.

Due to the intense media scrutiny of the world wide COVID-19 vaccination programme, more women may be anticipating and therefore noticing menstrual irregularities, which are normally very common. Menstrual irregularities have also been reported after other widely used vaccinations including HPV (human papillomavirus) and flu.

Some women have reported heavier and more frequent bleeding after the vaccination. This seems to be more common with the AstraZeneca vaccine than with the Pfizer vaccine. There are plausible reasons why there may be a link. 

A potential hypothesis for this is that an autoimmune reaction against platelets (now listed as a common side effect of the COVID-19 AstraZeneca vaccination) causes heavier bleeding. This is because platelets are needed to clot our blood, and lower platelets could mean heavier bleeding.

Dr Pat O’Brien, Vice President at the Royal College of Obstetricians and Gynaecologists, said:

“It’s important to remember these side effects are mild and should not deter women from having the vaccine when they are called. Many women will experience a temporary change in their periods from time to time during their lives. And right now, many women in their 30s are having the COVID vaccine. So it seems inevitable that in some women these two events will coincide by chance. If, however, these changes persist, or you have any new vaginal bleeding after the menopause, you should see your doctor.

We also want to stress that these perceived changes in menstrual cycle after having the COVID-19 vaccine should not be confused with an impact on fertility and the ability to have children. There is no evidence to suggest that COVID-19 vaccines will affect fertility.”

So… what next?

We believe the lack of information on this topic highlights the gender bias in clinical research trials towards men over women. We’d like to see menstrual irregularities investigated as part of clinical trials so women can be made aware of potential side effects, like changes to bleeding patterns, and so they can be prepared rather than anxious or worried. 

If we have learnt anything from The Lowdown community it is that women and their periods should not be ignored! Women would much rather be well-informed and empowered to anticipate and manage the side effects of life-saving vaccines, just like we are doing with contraceptive methods here at The Lowdown. 

The Lowdown are planning to conduct our own poll of our 20,000+ users for more stories about periods and the COVID-19 vaccination. Keep an eye on our Instagram feed for more information, and please let us know if and how your periods have been affected!

  1. Kloc M, Uosef A, Kubiak JZ, Ghobrial RM. Exaptation of Retroviral Syncytin for Development of Syncytialized Placenta, Its Limited Homology to the SARS-CoV-2 Spike Protein and Arguments against Disturbing Narrative in the Context of COVID-19 Vaccination. Biology (Basel). 2021;10(3):238. Published 2021 Mar 19. doi:10.3390/biology10030238 

  2. Royal College of Obstetricians and Gynaecologists. The RCOG and the RCM respond to misinformation around Covid-19 vaccine and fertility. January 2021. 

    Iacobucci G. Covid-19: No evidence that vaccines can affect fertility, says new guidance. BMJ  2021; 372 :n509 doi:10.1136/bmj.n509 

  3. Myriam Safrai, Benjamin Reubinoff, Assaf Ben-Meir. BNT162b2 mRNA Covid-19 vaccine does not impair sperm parameters. medRxiv 2021.04.30.21255690; doi: (pre-print not yet peer reviewed)

  4. British Fertility Society. Covid-19 vaccines and fertility. February 2021. 

  5. Li K, Chen G, Hou H, et al. Analysis of sex hormones and menstruation in COVID-19 women of child-bearing age. Reprod Biomed Online. 2021;42(1):260-267. doi:10.1016/j.rbmo.2020.09.020 

  6. MHRA. Coronavirus vaccine – weekly summary of Yellow Card reporting. June 2021. 

  7. BMJ. Rapid response to: Thrombosis after covid-19 vaccination. BMJ 2021;373:n958

  8. European Medicines Agency. Vaxzevria, COVID-19 Vaccine (ChAdOx1-S [recombinant]. 2021

  9. Identifier: NCT01978262. Immune and Hormone Response to Influenza Vaccine

  10. Suzuki S, Hosono A. No association between HPV vaccine and reported post-vaccination symptoms in Japanese young women: Results of the Nagoya study. Papillomavirus Res. 2018;5:96-103. doi:10.1016/j.pvr.2018.02.002 

  11. Shimabukuro, TT. Preliminary Findings of mRNA Covid-19 Vaccine Safety in Pregnant Persons. N Engl J Med 2021; 384:2273-2282 DOI: 10.1056/NEJMoa2104983

  12. Royal College of Obstetricians and Gynaecologists. COVID-19 vaccines, pregnancy and fertility. April 2021. 

  13. Royal College of Obstetricians and Gynaecologists. RCOG responds to reports that COVID-19 vaccine affects periods. May 2021

  14. Mattar CNZ et al. Addressing anti-syncytin antibody levels, and fertility and breastfeeding concerns, following BNT162B2 COVID-19 mRNA vaccination. 

One of The Lowdown’s fab Clinical Directors, Dr Frances Yarlett MBBCh (Hons) BSc (Hons) MRCP (2016) MRCGP DFSRH completed her medical training from Cardiff University in 2013. She is currently working as a salaried GP partner in Sheffield with an interest in complex medical patients and women’s health. Fran is really passionate about patient choice and wants to empower women to take control of their bodies and contraception needs.