DNA fragments in mRNA COVID-19 vaccines won’t harm you, as Florida surgeon general suggests

Florida’s top health official suggested without evidence that tiny DNA fragments in mRNA COVID-19 vaccines are dangerous and said the shots should not be used, but epidemiologists and vaccine researchers disagree.  

In a Jan. 3 statement, Dr. Joseph Ladapo, the state’s surgeon general, implied that recipients of the vaccine could pass on DNA fragments to their biological children.

"DNA integration poses a unique and elevated risk to human health and to the integrity of the human genome, including the risk that DNA integrated into sperm or egg gametes could be passed onto offspring of mRNA COVID-19 vaccine recipients," he said. "If the risks of DNA integration have not been assessed for mRNA COVID-19 vaccines, these vaccines are not appropriate for use in human beings."

Ladapo’s statement did not include any evidence that COVID-19 vaccines have caused "DNA integration," in which DNA fragments in the vaccines combine with a recipient’s DNA. 

Ladapo’s concerns are misguided, medical experts and FDA officials say. 

In early December, Ladapo wrote to U.S. Food and Drug Administration officials asking whether the agency had appropriately evaluated the potential risks posed by DNA fragments detected in some mRNA vaccine doses. The DNA fragments findings come from a 2023 preprint article that has been criticized for methodological flaws. (Preprint manuscripts have not been peer-reviewed or published in academic journals.) 

Ladapo argued that the vaccine’s lipid particles — which surround and protect the mRNA that  provides instructions for fighting COVID-19 to immune cells — are "an efficient vehicle for the delivery" of the mRNA into human cells, and "may therefore be an equally efficient vehicle for delivering contaminant DNA into human cells."

He asked the FDA whether it had evaluated the COVID-19 vaccine’s lipid nanoparticle delivery system for mRNA and expressed concern that the COVID-19 vaccine could cause "DNA integration in reproductive cells."

Ladapo pointed to a 2007 FDA guidance document he said included considerations about DNA integration that the agency recommended for vaccines that use DNA.  

But Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, wrote in a footnote to a Dec. 14, 2023, response to Ladapo that the nonbinding 2007 guidance "was developed for DNA vaccines themselves, not for DNA as a contaminant in other vaccines, and is not applicable to the mRNA COVID-19 vaccines."

Marks also wrote, "With over a billion doses of the mRNA vaccines administered, no safety concerns related to residual DNA have been identified." 

Pfizer, left, and Moderna bivalent COVID-19 vaccines are readied Nov. 17, 2022, for use at a clinic in Richmond, Va. (AP)

The COVID-19 vaccines work by introducing mRNA to teach cells to recognize the coronavirus’ spike proteins and equip the immune system to fight a COVID-19 infection. Because mRNA is fragile, the vaccines deliver the mRNA wrapped inside lipid nanoparticles. 

These fat particles protect the mRNA and "help it get taken up by specialized cells of the immune system," explained a Vaccine Makers Project video about mRNA vaccines. "Once inside these cells, the mRNA does not enter the cell’s nucleus or interact with DNA, but remains in the cytoplasm with other mRNA molecules, waiting to create the enzymes our body needs."

Experts said that small DNA fragments found in the vaccines are not cause for concern. Cells are needed to make vaccines, and those cells contain DNA. 

"Small amounts of residual DNA can be found in several approved vaccines, including influenza and hepatitis vaccines, which have been administered globally for more than 30 years," Pfizer spokesperson Kit Longley told PolitiFact in October.

Tiny DNA fragments from the COVID-19 vaccines’ starting material could wind up in the final vaccine, said Dr. Paul Offit, a pediatrics professor in the Children’s Hospital of Philadelphia’s infectious diseases division and director of its Vaccine Education Center.

In a video addressing concerns about these DNA fragments, Offit explained that the existence of DNA fragments does not pose a risk because it would be "virtually impossible" for those fragments to get into our DNA. 

"First, these DNA fragments would have to enter the cytoplasm, which is that part of the cell outside of the nucleus, and our cytoplasm hates foreign DNA," Offit said. 

In a Jan. 5 edition of the newsletter "Your Local Epidemiologist," three scientists said that when exposed to foreign DNA, our cells "destroy it through a shredder (called a DNase) — the DNA gets chopped into tiny fragments and our body recycles them."

Part of the COVID-19 vaccine manufacturing process includes treating the mRNA with that "shredder" to break down and eliminate any residual DNA, Marks wrote in his letter. As a result, he said the amount of residual DNA present in finished COVID-19 vaccines is well below the internationally agreed upon limits for biological products.

Even if a DNA fragment was injected into the body and reached a cell, it would have to enter a cell’s nucleus to alter DNA, Offit said. 

"It would have to cross the nuclear membrane, which requires a nuclear membrane access signal, which these DNA fragments don’t have," he said. If, somehow, the DNA did get into the nucleus, Offit said it would need an enzyme called "integrase" to integrate into a person’s DNA — and the fragments do not have this enzyme. 

In his response to Ladapo, Marks wrote that it is "quite implausible" that any residual DNA fragments could cross cells’ nuclear membranes and integrate with existing DNA — including the DNA in reproductive cells such as eggs or sperm. 

Marks also said studies in animals that have used the COVID-19 vaccines’ modified mRNA and lipid nanoparticle — and any "minute quantities of residual DNA fragments" — have found no evidence that the vaccines cause DNA or chromosomal damage, which is also known as genotoxicity. 

The data available after years of monitoring mRNA COVID-19 vaccine side effects in the millions of people who have been vaccinated "indicate no evidence indicative of genotoxicity," Marks wrote. 

Offit told PolitiFact the discussion of "DNA contaminants" in the COVID-19 vaccines is really one about "utterly harmless manufacturing residuals." Plus, he said people are exposed to foreign DNA all the time, including when they eat animal or plant products. 

PolitiFact Staff Writer Samantha Putterman contributed to this report.