Scientists' current knowledge about orthopox infections suggests that monkeypox reinfection following an infection or vaccine is unlikely—but some experts believe rare cases of reinfection may start to surface as more data becomes available.

Why monkeypox reinfection is unlikely

In studies of smallpox patients, researchers reported that immune cells that help the body fight the virus while killing infected cells remain in survivors' blood up to 83 years after they were infected. In addition, research suggests that neutralizing antibodies can be found in the body decades after an initial infection.

According to Paula Cannon, a professor of microbiology and immunology at the Keck School of Medicine at the University of Southern California, most viral diseases follow a similar pattern.

The Jynneos vaccine, currently authorized for monkeypox, is based on a weakened form of a similar virus called vaccinia virus, Cannon noted. "So you basically get an asymptomatic or incomplete infection, which will provide you with pretty high and complex levels of immunity."

Notably, data from vaccinia virus inoculations for smallpox suggest that the vaccine can provide reliable protection for at least five years, with some immunity for at least 10 years.

After several decades, researchers found comparable levels among vaccinated individuals and those who gained immunity from an infection. 

Will monkeypox reinfections surface in the future?

Currently, CDC is aware of just one report of a possible monkeypox reinfection, according to Brett Petersen, U.S. Public Health Service Deputy Chief for the Poxvirus and Rabies Branch, of CDC's National Center for Emerging and Zoonotic Infectious Diseases. However, Petersen noted that CDC expects reinfections to be a rare occurrence.

Still, real world data on monkeypox is still very limited. According to David Cennimo, an infectious disease expert at Rutgers New Jersey Medical School, it is possible that there will be reports of reinfections in the future.

"What we don't know is with this new outbreak, and the new epidemiology and route of transmission, whether that may impact some of what was previously seen with monkeypox and other related viruses, like smallpox. So, I think there's still more to learn there," Petersen noted.

"We don't have a lot of data on this, but we can extrapolate what we know about other orthopox infections, namely smallpox," said Jason Farley of the Johns Hopkins School of Nursing.

"Individuals who were infected with smallpox were protected from reinfection. There's likely a similar phenomenon that occurs with monkeypox, where people are not going to get reinfected—and definitely not immediately," Farley said.

According to Cennimo, it is possible that the immune memory could weaken several years after a monkeypox infection or vaccination.

"There may be some time over several years that somebody could get reinfected, or that their immunity wanes, or if they [become] immunosuppressed," Farley added. "In general, we expect most people to not be susceptible to reinfection in the near term, which I think will be useful when it comes to thinking about the trajectory of this outbreak in non-endemic countries."

For years, CDC has recommended that workers who come in close contact with smallpox or monkeypox get vaccinated every two or 10 years, respectively.

However, Cennimo noted that future recommendations will likely depend on the path of the current outbreak. "I couldn't predict if we're going to be telling patients getting the monkeypox vaccine now that in three years they're going to need a monkeypox booster," he said. "Certainly, if we don't control this transmission now, and this becomes an endemic infection, that may be the case." (Sheikh, New York Times, 9/8; Firth, MedPage Today, 6/30; Fernandez, Johns Hopkins panel, 8/12)