Possible links between the COVID-19 vaccine and preterm birth, menstrual disruptions, and increased risk of miscarriage have been evaluated here on The Pulse. Today, I’m back with another adverse effect to rule out: infertility. Read on for the research evidence behind the happy news that getting a COVID-19 shot is unlikely to disrupt your fertility, regardless of your gender, now or in the future.
First, you may have heard a rumor that a protein in the human placenta, called syncytin-1, might be affected by COVID-19 mRNA vaccines. This rumor started because syncytin-1, which is important for the formation of the placenta, was initially thought to be similar to the SARS-CoV-2 spike protein in shape. Since that rumor started circulating in 2021, several groups have looked into the science behind it to see whether there is any truth there.
The rumors are unfounded. It turns out that the SARS-CoV-2 spike protein is much bigger than the syncyntin-1 placental protein and these two proteins only share a very short sequence of protein building blocks (just four amino acids), suggesting that they are unlikely to be bound by the same antibodies. In fact, research published in the journal Cellular & Molecular Immunology showed that antibodies to the SARS-CoV-2 spike protein do not bind to syncytin-1 placental protein . And in a study published in the journal PLOS Biology, a group led by Alice Lu-Culligan showed that when they vaccinated mice against COVID-19, there was no increase in antibodies for (molecules that could bind to) syncytin-1 .
This finding has also been confirmed in people. In a study led by Paul Anantharajah Tambyah and published before peer review in the journal medRxiv, researchers showed that there were no antibodies against the syncytin-1 placental protein found in 15 frontline workers who had be vaccinated with the COVID-19 mRNA vaccine . Another study showed that there was no difference in embryo transfer success in women who were doing in vitro fertilization and had been vaccinated for COVID-19 . And in what’s called a cohort study, where researchers followed a group of more than 2,000 individuals over 10 months, vaccinated women got pregnant at similar rates as unvaccinated women .
That cohort study also showed that COVID-19 vaccination didn’t affect fertility in men, but what did temporarily affect fertility in men was SARS-CoV-2 infection . This finding is consistent with earlier results that demonstrated that, during and after SARS-CoV-2 infection, total sperm number decreases, despite no COVID-19 virus showing up in semen . While COVID-19 infection clearly affects sperm number, COVID-19 vaccination does not cause decreases in total sperm counts, according to a study published in the Journal of the American Medical Association .
So what is the bottom line? COVID-19 vaccination does not seem to negatively affect fertility and being vaccinated against COVID-19 does not cause sterility. The best thing you and your partner can do to protect yourselves and your future babies is to get vaccinated and stay current with vaccination recommendations. If you have questions or concerns about anything related to your pregnancy or your fertility, talk to your doctor or midwife. They can speak to your specific situation and health history, as well as discuss any concerns or issues that are on your mind.
- Prasad, M. et al. (2021). No cross reactivity of anti-SARS-CoV-2 spike protein antibodies with Syncytin-1. Cellular & Molecular Immunology, 18(11). doi:10.1038/s41423-021-00773-x
- Lu-Culligan, A. et al (2022). No evidence of fetal defects or anti-syncytin-1 antibody induction following COVID-19 mRNA vaccination. PLOS biology, 20(5), e3001506. doi:10.1371/journal.pbio.3001506
- Mattar, C. N. Z. et al. (2021). Addressing anti-syncytin-1 antibody levels, and fertility and breastfeeding concerns, following BNT162B2 COVID-19 mRNA vaccination. medRxiv,05.23.21257686; doi:10.1101/2021.05.23.21257686
- Morris, R. S. (2021). SARS-CoV-2 spike protein seropositivity from vaccination or infection does not cause sterility, F&S Reports, 2(3), doi:10.1016/j.xfre.2021.05.010
- Wesselink, A. K. et al. (2022). A prospective cohort study of COVID-19 vaccination, SARS-CoV-2 infection, and fertility, American Journal of Epidemiology, 191(8). doi:10.1093/aje/kwac011
- Best, J. C. et al. (2021). Evaluation of SARS-CoV-2 in Human Semen and Effect on Total Sperm Number: A Prospective Observational Study. The World Journal of Men’s Health, 39(3). doi:10.5534/wjmh.200192
- Gonzalez, D. C. et al. (2021). Sperm Parameters Before and After COVID-19 mRNA Vaccination. JAMA, 326(3). doi:10.1001/jama.2021.9976