Are COVID-19 Vaccines Going To Cause Infertility?

The short version: Someone has claimed that the COVID-19 vaccines are going to cause infertility because of a shared amino acid sequence in the spike protein of SARS-CoV-2 and a placental protein, which will make the immune system attack both as it can’t tell the difference. The truth? This sequence is too short for the immune system to meaningfully confuse it with placental proteins. It’s sort of like saying that you are going to be confused with a criminal because you wear a commonly sold red bracelet that was also found on the criminal. It’s not realistic. If this were true, we would also expect COVID-19 to cause early pregnancy loss a significant amount of the time. The evidence available to us does not support that this is the case. There is no reasonable basis to believe that vaccines against COVID-19/SARS-CoV-2 will affect fertility.

  1. T-2 independent (TI-2): Antigens that can cross-link a B cell receptor (immunoglobulin) to activate B cells without the need for T cell help. This mostly applies to carbohydrate antigens which have many repeating units of a sugar sequence.


  1. Adhikari, E. H., Moreno, W., Zofkie, A. C., MacDonald, L., McIntire, D. D., Collins, R. R. J., & Spong, C. Y. (2020). Pregnancy outcomes among women with and without severe acute respiratory syndrome Coronavirus 2 infection. JAMA Network Open, 3(11), e2029256
  2. Cosma, S., Carosso, A. R., Cusato, J., Borella, F., Carosso, M., Bovetti, M., … Benedetto, C. (2020). Coronavirus disease 2019 and first-trimester spontaneous abortion: a case-control study of 225 pregnant patients. American Journal of Obstetrics and Gynecology. doi:10.1016/j.ajog.2020.10.005
  3. Creasy, R. K., Resnik, R., Iams, J. D., Lockwood, C. J., Moore, T., & Greene, M. F. (2013). Creasy and resnik’s maternal-fetal medicine: Principles and practice (7th ed.). London, England: W B Saunders.
  4. Cunningham MW. 2019. Molecular mimicry, autoimmunity, and infection: The cross-reactive antigens of group A streptococci and their sequelae. Microbiol Spectr. 7(4). doi:10.1128/microbiolspec.GPP3–0045–2018.
  5. Dupressoir, A., Lavialle, C., & Heidmann, T. (2012). From ancestral infectious retroviruses to bona fide cellular genes: role of the captured syncytins in placentation. Placenta, 33(9), 663–671.
  6. Ewald DR, Sumner SCJ. 2018. Human microbiota, blood group antigens, and disease. Wiley Interdiscip Rev Syst Biol Med. 10(3):e1413.
  7. Faé KC, da Silva DD, Oshiro SE, Tanaka AC, Pomerantzeff PMA, Douay C, Charron D, Toubert A, Cunningham MW, Kalil J, et al. 2006. Mimicry in recognition of cardiac myosin peptides by heart-intralesional T cell clones from rheumatic heart disease. J Immunol. 176(9):5662–5670.
  8. Hemberger, M., Hanna, C. W., & Dean, W. (2020). Mechanisms of early placental development in mouse and humans. Nature Reviews. Genetics, 21(1), 27–43.
  9. Johnson, W. E. (2019). Origins and evolutionary consequences of ancient endogenous retroviruses. Nature Reviews. Microbiology, 17(6), 355–370.
  10. Komine-Aizawa, S., Takada, K., & Hayakawa, S. (2020). Placental barrier against COVID-19. Placenta, 99, 45–49.
  11. Maltepe, E., & Fisher, S. J. (2015). Placenta: the forgotten organ. Annual Review of Cell and Developmental Biology, 31(1), 523–552.
  12. Murphy K, Weaver C. 2016. Janeway’s Immunobiology. 9th ed. Boca Raton, FL: CRC Press.
  13. Podbilewicz, B. (2014). Virus and cell fusion mechanisms. Annual Review of Cell and Developmental Biology, 30(1), 111–139.
  14. Rotshenker-Olshinka, K., Volodarsky-Perel, A., Steiner, N., Rubenfeld, E., & H Dahan, M. (2020). COVID-19 pandemic effect on early pregnancy: are miscarriage rates altered, in asymptomatic women? Archives of Gynecology and Obstetrics. doi:10.1007/s00404–020–05848–0
  15. Rydyznski Moderbacher, C., Ramirez, S. I., Dan, J. M., Grifoni, A., Hastie, K. M., Weiskopf, D., … Crotty, S. (2020). Antigen-specific adaptive immunity to SARS-CoV-2 in acute COVID-19 and associations with age and disease severity. Cell, 183(4), 996–1012.e19.
  16. Sivaraman, H., Er, S. Y., Choong, Y. K., Gavor, E., & Sivaraman, J. (2020). Structural basis of SARS-CoV-2- and SARS-CoV-receptor binding and small-molecule blockers as potential therapeutics. Annual Review of Pharmacology and Toxicology, 61(1). doi:10.1146/annurev-pharmtox-061220–093932
  17. Snow EC, Noelle RJ, Uhr JW, Vitetta ES. 1983. Activation of antigen-enriched B cells. II. Role of linked recognition in B cell proliferation to thymus-dependent antigens. J Immunol. 130(2):614–618.
  18. Suchman, E. (n.d.). Cytopathic effects of viruses protocols. Retrieved December 3, 2020, from website:
  19. Turco, M. Y., & Moffett, A. (2019). Development of the human placenta. Development (Cambridge, England), 146(22), dev163428.
  20. Vance TDR, Lee JE. 2020. Virus and eukaryote fusogen superfamilies. Curr Biol. 30(13):R750–R754.
  21. Wadman, M. (2020). Why pregnant women face special risks from COVID-19. Science (New York, N.Y.). doi:10.1126/science.abe1694
  22. Yewdell JW, Dersh D, Fåhraeus R. 2019. Peptide channeling: The key to MHC class I immunosurveillance? Trends Cell Biol. 29(12):929–939.

I write about vaccines here. You can find me on Twitter @enirenberg and at (where I publish the same content without a paywall)