CLAIM: A Swedish study shows that Pfizer’s COVID-19 vaccine changes recipients’ DNA.

AP’S ASSESSMENT: False. The study tested whether the vaccine’s mRNA could be converted to DNA, and found that this was the case in certain lab-altered liver cell lines under experimental conditions. It did not assess whether the vaccine alters the human genome, or what the effects of that would be, according to experts and the study authors. Experts say additional research is needed because the findings in the lab setting cannot be used to make inferences about what might happen in a human body.

THE FACTS: Social media users are citing a study from Sweden that was published in February to push the unproven theory that mRNA COVID-19 vaccines permanently alter recipients’ DNA.

A clip being shared online in recent days shows three doctors, who have spread misinformation about the vaccines in the past, discussing the Swedish study and falsely claiming it demonstrates that “the Pfizer vaccine reverse transcribes and installs DNA into the human genome,” leading to harmful effects. The genome is the set of instructions to build and sustain a human being.

The clip comes from a longer roundtable discussion that was posted March 8 by Christian broadcasting network Daystar, during which faith leaders discussed COVID-19 vaccines with the doctors. Other social media users sharing the clip have commented that the paper proves mRNA COVID-19 vaccines “change the recipient’s DNA.”

Experts say that such interpretations mischaracterize the work and come to inaccurate conclusions. The study authors clarified their research in a Q&A in March after it received significant attention, stating “this study does not investigate whether the Pfizer vaccine alters our genome,” and that “there is no reason for anyone to change their decision to take the vaccine based on this study.”

“The results have in many cases been misinterpreted,” the Q&A also stated.

The study, conducted by researchers at Lund University in Sweden and published in a peer-reviewed journal, investigated the effect of Pfizer’s mRNA COVID-19 vaccine on a human cell line that was derived from liver cancer tissue. The experiment was conducted in a petri dish and aimed to answer the question of whether the mRNA in the vaccine could be converted to DNA.

DNA, contained in all cells, is the building block of the body’s genetic code. RNA is closely related to DNA, and one type, called messenger RNA or mRNA, sends instructions to the cell for different purposes. The mRNA in the COVID-19 vaccines helps train the body to recognize a protein from the coronavirus to trigger an immune response.

During the study, the researchers were able to detect DNA that had been converted from the vaccine’s mRNA in the lab-modified cell.

Some viruses, like HIV, are known to be able to convert RNA to DNA and then incorporate that DNA into host cells’ genome, which is one thing that makes the illness difficult to treat. Coronaviruses, however, are not expected to do this, said Bethany Moore, chair of the University of Michigan’s Department of Microbiology and Immunology.

Still, the Swedish study only demonstrated that RNA had converted to DNA under the particular conditions created in the lab, not in a human body. And this could be seen with natural virus infection as well, Moore said. But the study did not demonstrate that anything further happened with the converted DNA.

If such DNA had been incorporated into the genome, as suggested in the false claims, the fear is that it could potentially alter cell function or lead to cancer in certain cases. But that wasn’t observed in this study.

“Where that paper was getting a lot of press was the idea that those pieces of DNA were then getting incorporated into the genome, and there’s absolutely no evidence that that happened,” Moore said.

Moore also cautioned that the cells used in the study were “quite different than primary cells in the body.” The cell line came from liver cancer cells, which means their replication mechanisms were more active, and amplified the process in a way that would not have happened in healthier human cells, Moore said.

“In order to create these cell lines, the genetic make-up of the cells has to be ‘fiddled with’ to make them immortal and keep them alive in the petri dish,” Dr. David Strain, a senior clinical lecturer at England’s University of Exeter Medical School, wrote in an email to the AP. “These cells have had the normal protections of the immune system removed.”

Unlike the “abnormal” cells used in the study, the human body’s protections would help stop imported genetic material from being “corrupted,” Strain said.

“Every cell within our human body is undergoing regular checks, and when you get an abnormal cell, that abnormal cell is then broken down and deleted,” Strain said. “In the cell line in a petri dish, you don’t have those checks in place.”

Because the study design “does not necessarily reflect what happens” in most human bodies, he said the findings cannot be extrapolated to make inferences about what would happen in human subjects.

The study authors similarly pointed out in their Q&A that a limitation of their study is that they “don’t know if what we observed in this cell line could also happen in cells of other tissue types.” They stated that this would need to be addressed in follow-up studies.

“Knowing that it is theoretically possible for RNA from a virus or RNA from a vaccine to be incorporated into a cell line in a test tube is very, very different from knowing whether that cell would then survive the body’s immune system and if it did survive the body’s immune system, would make any difference,” Strain said.