Vaccines Didn’t Turn Back Mpox, Study Finds. People Did.

The News

The 2022 outbreak of mpox, previously known as monkeypox, was curbed in large part by drastic changes in behavior among gay and bisexual men, and not by vaccination, according to a new analysis published on Thursday in the journal Cell.

Mpox vaccinations in a mobile clinic outside a Manhattan club in 2022.Credit…Kholood Eid for The New York Times

Why It Matters: Vaccines often arrive too late to stamp out outbreaks.

Public health response to outbreaks often relies heavily on vaccines and treatments, but that underestimates the importance of other measures, said Miguel Paredes, lead author of the new study and an epidemiologist at the Fred Hutchinson Cancer Center in Seattle.

Although the Food and Drug Administration approved a vaccine for mpox in 2019, getting enough doses produced and into arms proved challenging for many months after the outbreak began. Vaccines for new pathogens are likely to take even longer.

The new analysis suggests an alternative. Alerting high-risk communities allowed individuals to alter their behavior, such as reducing the number of partners, and led to a sharp decrease in transmission, Mr. Paredes said. In North America, the outbreak began petering out in August 2022, when less than 8 percent of high-risk individuals had been vaccinated.

Public health messaging can “be really powerful to control epidemics, even as we’re waiting for things like vaccines to come,” he said.

The Long View: Vaccines are still important.

Some experts unrelated to the work were not convinced that behavioral change was largely responsible for stemming the outbreak.

“If the national numbers are driven by large outbreaks in a few places, then the folks at the highest risk in those places would get infected pretty quickly, and their immunity would be especially valuable in limiting the outbreak size,” said Bill Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health.

“Add in some vaccine-induced immunity in this group and a bit of behavior change, and it will be even more effective,” he said.

The Centers for Disease Control and Prevention worked closely with the L.G.B.T.Q. community to raise awareness about the importance of behavior modification, said Thomas Skinner, a spokesman for the agency.

While behavioral change can curtail outbreaks in the short term, vaccinations prevent the outbreak from resurging once people return to their normal routines, said Virginia Pitzer, an epidemiologist at the Yale School of Public Health.

“As we’ve seen with Covid, the behavioral change only lasts so long,” she said.