Daily Fact-Check: Have COVID-19 Vaccines Been Shown to Alter DNA, Cause Cancer?

The COVID-19 vaccines made by Pfizer/BioNTech and Moderna are produced with help from DNA templates, which include instructions for making the mRNA that encodes the spike protein. Manufacturers take steps to purify the final vaccine components, cutting up and removing the DNA, although there could be a very small amount of DNA left.

Past research and mechanistic logic indicate that any DNA remaining after these purification and quality control steps is likely inconsequential. However, in recent monthsunsubstantiated theories have spread online that DNA remaining in mRNA vaccines could integrate into a person’s own DNA and cause cancer, or even that the vaccines are already causing cancer.

A spokesperson from the U.S. Food and Drug Administration told us in an email that “no safety concerns related to residual DNA have been identified.” The spokesperson added that “with regard to the mRNA vaccines, while concerns have been raised previously as theoretical issues, available scientific evidence supports the conclusion that the minute amounts of residual DNA do not cause cancer or changes to a person’s genetic code.”

A spokesperson for the European Medicines Agency — which helps regulate medical products in the European Union — told us via email that the agency “can confirm that we have not seen any reliable evidence of residual DNA exceeding approved/safe levels” for the Pfizer/BioNTech or Moderna COVID-19 vaccines. Nor is the EMA “aware of scientific evidence showing that the very small amounts of residual DNA that may be present in vaccine batches could integrate into the DNA of vaccinated individuals,” the spokesperson continued.

Various experts also told us that it is unlikely that residual DNA in the vaccines could integrate into DNA or cause cancer, even in theory. And as we have previously written, there isn’t evidence to date that the vaccines cause cancer or have led to an increase in cancer.

Marc Veldhoen, an immunologist at the Instituto de Medicina Molecular João Lobo Antunes in Portugal, told us via email that residual DNA would be expected, but he refuted the idea that it could cause cancer. “Yes, there would be some fragments, but within the limit this is allowed and without any clinical consequence,” he said.

This family of claims was originally inspired by a preprint posted in April, which said there was “DNA contamination that exceeds” the EMA and FDA regulatory limits in Moderna and Pfizer/BioNTech vaccine vials sent anonymously to the authors in the mail without cold packs. This led to other reports of DNA in mRNA vaccine vials, including a second preprintthat analyzed largely expired vaccine vials obtained at pharmacies in Canada. None of this work has been published in peer-reviewed journals, and many elements of it have been criticized.

We reached out to Kevin McKernan, an author on both preprints, to better understand his views. Rather than replying to our email, he posted a screenshot of it on X, formerly known as Twitter, and included responses there. McKernan, who has an undergraduate degree in biology, is the founder of Medicinal Genomics, a company that markets test kits and genomics-related services to the cannabis, hemp and mushroom industries.

Some of the alleged concern has focused on the possibility, raised in the original preprint, that some of the residual DNA in the Pfizer/BioNTech vaccine is from a monkey virus called SV40. The EMA confirmed to us that the plasmid, or DNA template, used to make the Pfizer/BioNTech vaccine contains some short sections of DNA from this virus. A Pfizer spokesperson also told us via email that “specific, non-infectious parts of the SV40 sequence, which are commonly used in the pharmaceutical industry are present in starting material used by Pfizer and BioNTech.”

But none of the sequences identified in the preprint are known to cause cancer, contrary to recent social media posts that say “SV40, a cancer causing sequence” was “put in the Covid Vaccine.”

Experts say there isn’t reason to think that any small pieces of leftover DNA, including SV40 DNA, in the vaccines would be harmful. 

“It is very unlikely that any residual DNA would integrate into a person’s genome and if it did it would be even much less likely to cause cancer,” Barry Milavetz, a molecular biologist who studies SV40 at the University of North Dakota, told us in an email.