Can mRNA COVID-19 vaccine affect fertility or affect future babies?
There is no biologically plausible reason why this vaccine could have any effect on our genes or fertility and there is strong evidence it does not.
Vaccination is recommended before and during pregnancy
Women who are trying to become pregnant need not to delay the vaccination nor avoid becoming pregnant. COVID-19 is a potentially very serious disease. Pregnant women and their unborn babies are greater risk of needing hospital care than women who are not pregnant
Comirnaty and fertility
Shortly after the Pfizer mRNA vaccine, Comirnaty, became available overseas misinformation circulated on social media about negative effects on fertility of vaccinated women. Such statements are misleading and calculated to cause unnecessary fear. There is no plausible reason why this vaccine (or any previously) could have such effects and there is strong evidence that is does not.
Every new vaccine or new medicine is tested thoroughly before it can be given to humans, to check for any potential harms prior to conception, during pregnancy or to the baby. If a vaccine candidate fails this stage of testing, further research will be stopped.
Animal studies have shown no effects on fertility – for this vaccine or other the COVID-19 vaccines approved in New Zealand. For example, when female rats were given very large doses of the Pfizer COVID-19 vaccine (300 times the human dose) before mating and during pregnancy, no changes were seen in mating performance, fertility or any ovarian or uterine measurement. In addition, no effects were seen before or after birth on the survival, growth, physical development or neurofunctional development of the babies.
The vaccine is short-lived
Comirnaty vaccine contains messenger ribonucleic acid (mRNA) inside a fatty bubble which is delivered to muscle cells in the arm when you are vaccinated. The mRNA and its protective bubble are very fragile, so that it needs to be stored at very cold temperatures to stop it from degrading.
Once outside of its lipid bubble, mRNA is quickly destroyed by enzymes (ribonucleases) found everywhere, including inside and outside of our cells. It only has a day or two to do its work. The components of the lipid bubble are also cleared from our body as a waste product. The vaccine gives the body the recipe to make replicas of the COVID-19 virus spike protein and is completely gone within a couple of days.
The quantity of this protein produced after vaccination is much lower than the amount seen in people with COVID-19 infection with the virus spreading throughout their body. Furthermore, as soon as it is produced, this protein is dismantled inside specialist cells and the pieces are shown to the immune system in the lymph nodes nearest to the arm muscle.
The ovaries and testes are protected.
The ovaries or testicles are protected, from infection and damage, by special cells (such as Sertoli cells in males and columnar epithelial cells in females) which prevent cells of the immune system or antigens (such as parts of any vaccine) from entering.
Evidence from fertility clinics
In Israel, patients attending fertility clinics have been carefully studied after having the Comirnaty vaccine. No difference in the in vitro fertilisation (IVF) cycle outcomes, including the number of eggs collected; the number of matured eggs; the fertilisation rate; and the number and quality of embryos at day 3, were seen in women who had intracytoplasmic sperm injections (ICSI) before and after two doses of Comirnaty (time from first dose 57± 24 days). Additionally, the number and percentage of clinical pregnancies did not differ significantly between the pre and post vaccination groups. Another study, which looked at women having eggs collected shortly after vaccination (mean 12 days among those having had one dose and 49 days after first dose among those having had two doses), found no differences in follicular function, including hormone production, and oocyte (egg) quality biomarkers. In addition, sperm parameters including semen volume, sperm concentration, sperm motility, and total motile sperm count have been the same in men following vaccination (33 days after first dose). Studies in America have also found no differences in embryo implantation or early pregnancy development nor sperm parameters.
Vaccinated women can fall pregnant
As well as this detailed information about the lack of impact on factors related to fertility, the real-world experience with the vaccine is also reassuring. Numerous women have conceived following Comirnaty vaccination. Looking at participants in the v-safe pregnancy registry in the US, found no difference from the expected spontaneous abortion rate in women who received an mRNA vaccine from 30 days before the first day of their last menstrual period through to 14 days after (NIH preprint).
Any alleged similarity between the SARS-CoV-2 spike protein and the human protein, syncytin-1, has been completely disproven. Any amino acid sequences in common are much too short to activate an immune response. Furthermore, antibodies in the serum of women previously infected with COVID-19 cannot recognise or bind to syncytin-1.
Some women have reported their menstrual periods may be early or heavy following the vaccination. This is possible since there is a connection between the immune system and the bleeding of menstrual cycles, but such changes can also occur coincidentally or due to anxiety that some people experience when being vaccinated. Any potential effect is brief and will not affect long term fertility. There is no effect on the placenta during pregnancy because different biological processes maintain the uterus lining.
- Bentov Y, Beharier O, Moav-Zafrir A, et al. Ovarian follicular function is not altered by SARS-CoV-2 infection or BNT162b2 mRNA COVID-19 vaccination. Hum Reprod. 2021;36(9):2506-13. doi: 10.1093/humrep/deab182
- 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. Reproductive Toxicology. 2021;103:28-35. doi: https://doi.org/10.1016/j.reprotox.2021.05.007
- Gonzalez DC, Nassau DE, Khodamoradi K, et al. Sperm parameters before and after COVID-19 mRNA vaccination. JAMA. 2021;326(3):273-4. doi: 10.1001/jama.2021.9976
- Zauche LH, Wallace B, Smoots AN, Olson CK, Oduyebo T, Kim SY, et al.. Receipt of mRNA COVID-19 vaccines preconception and during pregnancy and risk of self-reported spontaneous abortions, CDC v-safe COVID-19 Vaccine Pregnancy Registry 2020-21. 2021;
- Morris RS. SARS-CoV-2 spike protein seropositivity from vaccination or infection does not cause sterility. F&S Reports. doi: 10.1016/j.xfre.2021.05.010
- Safrai M, Herzberg S, Imbar T, Reubinoff B, Dior U, Ben-Meir A. The BNT162b2 mRNA Covid-19 vaccine does not impair sperm parameters. Reproductive BioMedicine Online 2022;44(4):685–8.
Preprint papers, not peer-reviewed
- Safrai M, Rottenstreich A, Herzberg S et al. Stopping the misinformation: BNT162b2 COVID-19 vaccine has no negative effect on women’s fertility medRxiv preprint [accessed 13 Sep 2021; posted 01 June 2021] doi: 10.1101/2021.05.30.21258079