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No evidence that COVID-19 vaccine results in sterilization

December 8, 2020 GMT

CLAIM: The head of research at Pfizer says the COVID-19 vaccine causes female sterilization because it contains a spike protein known as syncytin-1.

AP’S ASSESSMENT: False. The Pfizer and BioNTech COVID-19 vaccine does not contain the protein syncytin-1, which is important for the creation of placenta. The head of research at Pfizer made no such claim. 

THE FACTS: Social media users are sharing a screenshot from an article titled “Head of Pfizer Research: Covid Vaccine is Female Sterilization” to claim the vaccine results in sterilization of women. Information in the article, carried by the blog “Health and Money News,”  is attributed to Michael Yeadon, a retired British doctor who left Pfizer nine years ago. Attempts to reach Yeadon were unsuccessful. 


The article says “the vaccine contains a spike protein called  syncytin-1, vital for the formation of human placenta in women.” It goes on to say “the vaccine works so that we form an immune response AGAINST the spike protein, we are also training the female body to attack syncytin-1, which could lead to infertility in women of an unspecified duration.”

Posts carrying the false information shared a petition filed by Yeadon and Wolfgang Wodarg, a German physician, to the European Medicines Agency that demanded that clinical trials of the Pfizer vaccine be stopped in the European Union until more safety and efficacy data can be provided. In the petition, the two acknowledge that there is no indication “whether antibodies against spike proteins of SARS viruses would also act like anti-Syncytin-1 antibodies.”

“However if this were to be the case this would then also prevent the formation of a placenta which would result in vaccinated women essentially becoming infertile,” the petition says. 

Experts say there is no evidence that the Pfizer vaccine would result in sterilization of women. 

Rebecca Dutch, chair of University of Kentucky’s department of molecular and cellular biochemistry, said in an email that while syncytin-1 and the spike protein broadly share some features, they are quite different in the details that antibodies recognize.  

Aside from the fact that COVID-19’s spike protein and syncytin-1 are viral fusion proteins that cause membrane fusion, they are not related at all, Dutch said. Additionally, the vaccine being developed by Moderna, like the one being developed by Pfizer and BioNTech, rely on messenger mRNA, which tells the body how to make the spike protein and trains the immune system to identify the real virus. They do not contain syncytin-1. 


“The idea behind this technology is that both of these vaccines contain the sequence of the RNA that encodes for the spike protein of SARS-COV2,” said Matthew Frieman, associate professor of microbiology and immunology at the University of Maryland School of Medicine. 

Jacob Yount, an associate professor of the department of microbial infection and immunity at Ohio State University, College of Medicine, has studied the syncytin proteins as well as SARS-CoV-2. Yount said the COVID vaccines do not contain syncytin-1 protein or mRNA encoding syncytin-1, and thus there is no reason to think that an immune response against syncytin-1 would be developed. 

“We don’t see infertility with the flu vaccine and that is also targeting a viral fusion protein in a similar way that the spike is a viral fusion protein of the coronavirus,” he said. 

Anti-vaccine advocates shared the false post online, encouraging others to spread the information. Yount said he became aware of the false claim when someone sent it to him on Facebook.

Pfizer spokeswoman Jerica Pitts confirmed to The Associated Press that their vaccine candidate has not been found to cause infertility. 

“It has been incorrectly suggested that COVID-19 vaccines will cause infertility because of a shared amino acid sequence in the spike protein of SARS-CoV-2 and a placental protein,” she said in an email. “The sequence, however, is too short to plausibly give rise to autoimmunity.”


This is part of The Associated Press’ ongoing effort to fact-check misinformation that is shared widely online, including work with Facebook to identify and reduce the circulation of false stories on the platform.

Here’s more information on Facebook’s fact-checking program: