Pfizer’s Covid-19 vaccine does not cause birth defects

17 February 2022
What was claimed

You are not meant to have unprotected sex after a second dose of the Pfizer Covid-19 vaccine as it could cause birth defects due to genetic manipulation.

Our verdict

This is not advice for everyone who’s had the Pfizer vaccine. There is no evidence the vaccine causes birth defects. This was a precaution in the vaccine trial, as is standard in many trials, to prevent participants conceiving shortly afterwards, but there was no suspicion of a link with birth defects.

A Facebook post claims that a Pfizer document advises people not to have unprotected sex within 28 days of the second dose of its Covid-19 vaccine, because of the supposed risk of “birth defects due to genetic manipulation”.

This is not true.

The post contains a very blurry screenshot of what appears to be a Pfizer document that contains the rules for participants in its clinical trial in 2020—not for ordinary people receiving the vaccine.

It is standard practice in new drug and vaccine trials to ensure participants are not pregnant and avoid conceiving.

There is no evidence of a risk of birth defects from Pfizer’s Covid vaccine, or from any of the others.

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What does the post say?

The Facebook post includes a screenshot of a real Pfizer document, which outlines how the trial of its Covid vaccine will be conducted.

The screenshot shows page 132, which gives “contraceptive guidance” to men and women participating in the study. It says that men must not donate sperm, and that neither men nor women “of childbearing potential” should have unprotected sex for at least 28 days after receiving the second dose. The guidance says this “corresponds to the time needed to eliminate reproductive safety risk of the study intervention(s)”.

The Facebook post highlights this section and adds the caption: “births [sic] defects due to genetic manipulation”.

However, the same document also explains that the contraceptive guidance is a precaution because of a lack of data, and there is no reason to think that the vaccine might cause birth defects.

On page 39, it says: “Human reproductive safety data are not available for BNT162 RNA-based COVID-19 vaccines [like Pfizer’s], but there is no suspicion of human teratogenicity [causing birth defects] based on the intended mechanism of action of the compound. Therefore, the use of a highly effective method of contraception is required.”

Contraceptive guidance is a standard part of the trial design for a new drug around the world, even when no toxic effect is expected.

The National Institute of Allergy and Infectious Diseases told the US fact checker Check Your Fact: “Clinical trials of investigational products—those that have not yet been approved or authorized by the FDA [US Food and Drug Administration]—always include a contraceptive requirement unless the same product has been used extensively for a different purpose with a proven safety record in pregnancy.”

No evidence the vaccine affects fertility

The Medicines and Healthcare products Regulatory Agency in the UK says: “There is no evidence to suggest that COVID-19 vaccines will affect fertility and your ability to have children.”

Initially, the vaccines were not recommended for all pregnant women as a precaution, when they first became available in 2020, but this advice changed in April 2021, when real-world evidence showed no safety concerns in pregnancy. More than 100,000 pregnant women have now been vaccinated with the Pfizer or Moderna vaccines in the UK, and they are safe to use in pregnancy.

We’ve written a series of articles about the Covid vaccines and pregnancy, which has been a common theme for misinformation during the pandemic.

Photo by Kelly Sikkema on Unsplash


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