One of the main drivers of vaccine hesitancy is the potential effects on fertility and pregnancy outcomes, a common fear women especially share. But is such concern true? No, they are not true, as far as what existing research has shown.
Animal studies have confirmed that the Covid-19 vaccines, at least for Pfizer’s and Moderna’s mRNA, have no effects whatsoever on the ovaries, both microscopically and macroscopically. This indicates that Covid-19 mRNA vaccines won’t cause any long-term harm to the ovaries. If ovarian toxicity is present, visible tissue damage would occur, but the animal experiments noted no such damage.
As stated in the European Medicines Agency (EMA) assessment report of Pfizer’s mRNA vaccine (page 47 out of 140):
Total recovery (% of injected dose) of radiolabeled LNP+modRNA outside the injection site was greatest in the liver (up to 21.5%) and was much less in spleen (≤1.1%), adrenal glands (≤0.1%) and ovaries (≤0.1%). No evidence of vaccine-related macroscopic or microscopic findings were found in the ovaries in the repeat-dose toxicity studies…and no effects on fertility were identified in the DART study….Given the current absence of toxicity in the DART data, the absence of toxicological findings in gonads in the repeat-dose studies and that the radioactivity in the gonads were low (below 0,1% of total dose), the current data does not indicate it to be a safety concern. The relative high dose used in the rats (500x margin to human dose based on weight) also supports a low risk from distribution to the gonads in humans.
*LNP+modRNA refers to lipid nanoparticle-encapsulated mRNA; DART study is developmental and reproductive toxicology study, where researchers inject the mRNA vaccine into rats and measure various outcomes related to fertility and reproduction; gonads are the main reproductive organs in males (testes) and females (ovaries).
Similarly, the EMA assessment report of Moderna’s mRNA vaccine also presented the DART study on rats, finding no effects on ovarian anatomy, female fertility, pregnancy outcomes, and offspring development.
In PubMed, searching the keywords (covid* OR sars-cov-2) AND vaccin* AND (ovar* OR fertili*) returned several studies of relevance:
- Wesselink et al. performed a cohort study covering residents in America and Canada, and reported that Covid-19 vaccination was not associated with infertility with either sex compared to no vaccination. However, prior Covid infection was associated with reduced fertility in men, but not women, compared to no infection.
- Wainstock et al. also performed a cohort study in Israel, finding that Covid-19 vaccination was not associated with any changes in pregnancy outcomes or changes in delivery and newborn complications compared to no vaccination.
- Hillson et al. examined the pregnancy rates and outcomes in phase I, II, and III clinical trials of AstraZeneca’s DNA vaccine, noting no significant differences between vaccinated and placebo groups. Thus, vaccinated women were not any less fertile than the control group.
- Bentov et al. showed that Pfizer’s mRNA vaccine elicited an immune response, but it doesn’t affect ovarian functions, indicated by hormone levels and oocyte (egg) quality, compared to the unvaccinated group.
- Orvieto et al. examined women undergoing ovarian stimulation for in vitro fertilization, in which vaccination status (Pfizer’s mRNA) did not affect ovarian reserve or the number of good-quality eggs.
- Bowman et al. found that Pfizer’s mRNA vaccine (at a >300-times higher dose than the human dose) did not affect fertility, mating performance, or any ovarian functions. The vaccine also did not affect the rats' embryo, fetal, or offspring development.
- Stebbings et al. found no effects of AstraZeneca’s DNA vaccine (at a higher dose than human use) on female fertility, mating performance, and pregnancy course and outcomes in mice.
Overall, these studies show that the Covid-19 vaccines don’t affect ovarian function or fertility. Although birth rates dropped in many countries in Europe, they are up by 4% in the U.S., 5% in New Zealand, and 16% in Ireland, which are also countries that use mRNA vaccines.
If the mRNA vaccine causes infertility, it should cause infertility in every country and we should see declining birth rates in every country, but we don't.
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