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A health worker administers a dose of COVID-19 vaccine during a vaccination clinic in Reading, Pa. 

CLAIM: Pfizer has acknowledged in a statement it conducted “gain of function” research as part of its development of a vaccine and a separate medical treatment for COVID-19.

THE FACTS: Experts said nothing in a recent statement by the company suggests it’s conducting research designed to make COVID-19 more harmful, as some social media users claim. A statement released Jan. 27 by Pfizer in response to allegations it was conducting risky “gain of function” research triggered another round of false speculation against one of the top makers of COVID vaccines.

Gain of function refers to scientific experiments that give an organism a new property or enhances an existing one. In the case of a virus such as the coronavirus that causes COVID-19, that could involve making it more harmful, or giving it the ability to transmit to other species. But the company said no such things in its statement, stressing that its vaccine-related experiments are undertaken only after a new variant has been identified by public health authorities.

“This research provides a way for us to rapidly assess the ability of an existing vaccine to induce antibodies that neutralize a newly identified variant of concern,” the company said. “We then make this data available through peer reviewed scientific journals and use it as one of the steps to determine whether a vaccine update is required.”

For research related to its antiviral medication Paxlovid, Pfizer said that “most” of the work is conducted using computer simulations or mutations of a non-infectious part of the virus. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston, Texas, said nothing in the statement suggests Pfizer is conducting research designed to “weaponize” COVID-19 or “increase its pathogenicity,” as some social media users claim.

“They might be undertaking virologic research to test the limits of their technologies knowing that through virus evolution some of these changes may occur naturally,” he wrote in an email. Benjamin Neuman, a virologist at Texas A&M University, agreed, though he said Pfizer’s statement is “written in a technical way” that could have been “made clearer for non-science readers.”

“To be gain of function, the researcher needs to deliberately make a change, knowing that change makes the virus more dangerous, and the change must be something the virus could not reasonably do on its own,” Neuman wrote in an email. “Miss out any part of that definition, and it’s not gain of function. That’s a really high bar, and the last part is the key.”

Albert Ko, who chairs the epidemiology department at the Yale School of Public Health in New Haven, Connecticut, said the online claims amounted to “scare mongering.”

“Engineering the virus does not always mean gain of function research,” he said. “Vaccines are made this way, from taking pieces of one virus and placing it into another virus. It does not necessarily mean a high risk of creating a stronger, more dangerous virus.”

At the same time, he said, the company should disclose more information about the work, such as its internal approvals process and safety protocols. A spokesperson for Pfizer declined to respond to requests for additional comment.

“The statement stands as our comment on the false allegations currently being made about vaccine research at Pfizer,” Amy Rose wrote in an email.

— Associated Press writer Philip Marcelo in New York contributed this report.