'No evidence' COVID-19 vaccines cause infertility

·6 min read

As state and federal officials work to expedite the distribution of the Moderna and Pfizer vaccines to health care workers and long-term care facility residents, experts worry that a dangerous myth linking the COVID-19 vaccines to infertility may further hinder efforts to deliver them safely and quickly. Facebook has since flagged posts containing the myth, labeling them “false information” — and in a statement to Yahoo Life, a spokesperson for Pfizer denied the claims. But to help clear up any confusion, here’s a breakdown of what you need to know.

Where did the idea that COVID-19 vaccines cause infertility come from?

The myth originated in a letter written by two scientists that was later shared to Facebook in posts claiming that the “head of research at Pfizer” said the vaccine “causes female sterilization” because it contains a protein crucial for placenta development. Later iterations of the myth claimed that the vaccine may not contain that placental protein (known as syncytin-1) but that the genetic sequence it contains is so similar to the placental protein that it will confuse the body into attacking them both.

A myth suggesting COVID-19 vaccines may cause infertility is circulating on Facebook. Here's why experts say the claim is baseless. (Getty Images)
A myth suggesting COVID-19 vaccines may cause infertility is circulating on Facebook. Here's why experts say the claim is baseless. (Getty Images)

What is wrong with this theory?

For one, the purported source of the information is incorrect. The concept was not floated by Pfizer’s head of research but by two non-Pfizer-affiliated individuals: One is a scientist named Michael Yeadon who left Pfizer 10 years ago and has made multiple baseless claims about the pandemic, including one in November when he declared that the pandemic was “effectively over” and that vaccines were unnecessary. His co-author is a German physician named Dr. Wolfgang Wodarg, who has similarly spread misinformation during the pandemic, including a video in late April in which he called COVID-19 “harmless.”

Beyond the misattribution, experts say the claims themselves are false. “Rumors saying that they’re using the placenta protein instead of the spike protein, that’s just flat-out wrong,” says Richard Kennedy, an immunologist and co-director of the Mayo Clinic’s Vaccine Research Group. Kennedy says the idea that the genetic sequence of the spike protein is very similar to the genetic sequence of syncytin-1 is also wrong. “The amount of similarity is minute,” says Kennedy.

What is the “spike protein” referring to, and why is it important?

Both Pfizer’s and Moderna’s vaccines use a novel approach to immunity known as messenger RNA (mRNA), which — contrary to fear-mongering Facebook posts — is considered to be safer than previous vaccines. Instead of relying on live or deactivated virus, the mRNA vaccines use the genetic sequence of the spike protein, which is found on the surface of the SARS-CoV-2 virus, to trigger an immune response.

As the Centers for Disease Control and Prevention explains, the instructions to build the spike protein allow the body to “recognize that the protein doesn’t belong there and begin building an immune response and making antibodies.” It’s a process that is not only quicker and less expensive than vaccines containing a virus but also more precise. As with any vaccine, there is a chance that rare complications may emerge, but in the seven years that the technology has been tested on humans, no long-term side effects have been reported.

How do we know it doesn’t resemble the placenta protein?

Kennedy says that the spike protein has roughly 1,300 amino acids, which fold together to form the protein; out of these, just four overlap with syncytin-1. “I tried an online tool that compares protein sequences — it couldn’t even line the two proteins up to compare them, that is how dissimilar they were,” he says. Furthermore, if the spike protein was somehow similar enough to syncytin-1 to prompt the immune system to attack them both, then all women who contracted COVID-19 would be infertile.

“The spike protein is not limited to just the vaccine,” says Kennedy. “[If this myth were true], that would mean that every single person infected with COVID-19 would have an immune response to the same spike protein, and therefore they would all be infertile as well.” Over a year into the pandemic, researchers have found no evidence that COVID-19 causes infertility in women. In fact, a study published in JAMA in November compared pregnancy outcomes in women who developed severe COVID-19 and those who tested negative for the virus, concluding: “SARS-CoV-2 infection in pregnancy is not associated with adverse pregnancy outcomes.”

What have Pfizer and Moderna said about the claims?

In a statement to Yahoo Life, a spokesperson for Pfizer said there is “no data” to support this hypothesis. “It has been incorrectly suggested that COVID-19 vaccines will cause infertility because of a very short amino acid sequence in the spike protein of SARS-CoV-2 that is partly shared with the placental protein, syncytin-1,” the spokesperson wrote. “The sequence, however, is so short, not even 4 amino acids in a row, but rather 4 shared amino acids in a sequence of 5 that it is very unlikely that it could lead to the body generating an immune response that would result in the body attacking itself or the placenta.” Moderna did not reply to Yahoo Life’s request for comment.

So is it safe for those wanting to get pregnant to take a COVID-19 vaccine?

Kennedy says there is no reason to believe vaccines are unsafe for women wanting to get pregnant. “There were 23 women in Pfizer's trial and 13 in the Moderna trial that were pregnant,” he says, noting that typically these trials don’t involve pregnant women, but that they were either missed during screening or became pregnant later. “None of them had any issues. There was a spontaneous abortion in the Pfizer trial, but that was in someone that got a placebo, and two abortions in Moderna, both of them in the placebo.”

On top of that, other experts have noted that actually contracting COVID-19 during pregnancy does come with risks. “Pregnant people are at an increased risk for severe illness from COVID-19 and death,” the CDC notes on its website. For all of these reasons, Kennedy says that individuals should think twice before believing what they read on social media. “I suggest being very careful as to what information you choose to believe and ... and disbelieve,” says Kennedy. “You should vet the information and the sources very carefully. A random Facebook post from a stranger is probably less reliable than talking to an expert, your physician or health care provider.”

For the latest coronavirus news and updates, follow along at https://news.yahoo.com/coronavirus. According to experts, people over 60 and those who are immunocompromised continue to be the most at risk. If you have questions, please reference the CDC’s and WHO’s resource guides.

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