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There’s no evidence that vaccines can affect fertility. What do we know so far?

This article was published on
August 10, 2021

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To-date, there is no data that the COVID-19 vaccines affect fertility. Research is ongoing to continue studying the relationship between COVID-19 vaccines and fertility long-term, and to make sure there are no risks. Many experts say that COVID-19 is more harmful for pregnant individuals and potentially for those who are hoping to become pregnant than the vaccines that protect against it. 

To-date, there is no data that the COVID-19 vaccines affect fertility. Research is ongoing to continue studying the relationship between COVID-19 vaccines and fertility long-term, and to make sure there are no risks. Many experts say that COVID-19 is more harmful for pregnant individuals and potentially for those who are hoping to become pregnant than the vaccines that protect against it. 

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What our experts say

Currently, no data suggest that any of the COVID-19 vaccines cause infertility in men or women. 

Scientists are collecting data to continue studying the relationship between COVID-19 vaccines and fertility to make sure that the vaccines do not pose any risk or potential harm to fertility. So far, no data suggests any harm or risk. 

One study done on COVID-19 vaccines and fertility in men compared sperm fertility before and after two doses of COVID-19 vaccines. The study did not find any significant differences. However, the study had a small sample size and only looked at the vaccine’s short-term effects. More studies and more long-term data collection are needed to continue to evaluate the link between male fertility and the COVID-19 vaccines. 

It is also worth noting that even though semen analysis is the best predictor of male fertility, it is not a perfect predictor of fertility. More studies that use other predictors will help to further our understanding of the relationship between COVID-19 vaccines and fertility.   

There is also no data to suggest that COVID-19 vaccines affect fertility among women. One study recently conducted compared how likely an embryo was to implant across three groups of women. When an embryo is planted, that means pregnancy has started. The three groups were: 

1) women who were vaccinated 2) women who had been infected with COVID-19 3) women who were neither vaccinated nor had never been infected with COVID-19

The study did not find significant differences in the ability to start pregnancy (or the “embryo implantation rates”) across the three groups, indicating that the vaccines did not have an impact on fertility.

Some individuals also became pregnant during clinical trials of the Pfizer and Moderna COVID-19 vaccines, suggesting that the vaccines did not affect fertility in those individuals. Among those pregnancies, there have been no documented increases in miscarriages or newborns with health issues present at birth. 

Research shows that newborns may in fact benefit from mothers getting COVID-19 vaccines. In one study done at Cornell University, research found that 99% of newborns had antibodies after their mothers received both vaccine doses, giving them protection from the virus at birth. 44% of babies had antibodies after one dose.

Other studies conducted in women have focused on the COVID-19 virus and immunity-building antibodies during pregnancy. Research shows that COVID-19 antibodies can be transferred across the placenta in mothers who had COVID-19 at some point. This suggests that newborns of mothers who test positive for virus antibodies, or who have tested positive for the COVID-19 virus, may have some protection against COVID-19 at birth.

Context and background

The American College of Obstetrics and Gynecologists (ACOG) have advised all women above 18 years old, women planning to get pregnant, all pregnant women, and lactating mothers to get vaccinated. ACOG also has cautioned pregnant women about the risks of getting COVID-19 while pregnant.

Some online claims misleadingly assert similarities between part of the COVID-19 virus (the spike protein) and a human protein involved in the development of the placenta. The false claims suggest that as a result of this similarity, the vaccines will attack fertility functions. Several geneticists, immunologists, and biochemists have looked at the sequences of both proteins and concluded that there are no meaningful similarities between the COVID-19 spike protein and the human protein involved in placenta development.

Resources

  1. Expert reaction to study looking at COVID-19 and male reproductive function (Science Media Center)
  2. Zika virus infection in semen: effect on human reproduction (The Lancet Infectious Diseases)
  3. COVID-19: No evidence that vaccines can affect fertility, says new guidance (The BMJ)
  4. Sperm Parameters Before and After COVID-19 mRNA Vaccination (JAMA)
  5. 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)
  6. Placental protection (Harvard Medical School)

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