Health officials: U.S. faces 'substantial risk' of mpox resurgence this summer

Summer could see a resurgence of an outbreak of mpox, the virus formerly known as monkeypox, unless more of those at risk get vaccinated, government officials warned Thursday.

Estimates of vaccine effectiveness range from 36% to 75% after one dose and 66% to 86% after two doses, according to data released Thursday, said Dr. Christopher Braden, the Centers for Disease Control and Prevention’s mpox response incident manager.

Men who have sex with men continue to constitute most cases of the virus, which causes painful lesions but is almost never deadly. The CDC’s latest Morbidity and Mortality Weekly Report said that male-to-male sexual contact drove last year's outbreak.

The figures released Thursday relate to a post-vaccination reduction in symptomatic infection, not necessarily a reduction in transmission of the virus, Braden said. Measuring the effect on spread, he said, is more difficult. 

The recommended vaccine, Jynneos, is administered in two doses several weeks apart.

Starting in spring 2022, the virus began to show up in geographic areas where it had been rare — the United States and Europe, beyond Central and West Africa, where it has long been endemic — and soon became a declared global emergency. New York City was the outbreak's epicenter, and the state Health Department also focused on vaccination in Suffolk County because it is home to gay vacation communities on Fire Island.

A year later, there is reason for concern about a resurgence, particularly with LGBTQ Pride celebrations happening this month, and the at-risk population, estimated to be about 1.7 million Americans, should be vaccinated, Dr. Demetre Daskalakis, the White House national mpox response deputy coordinator, said Thursday.

“Without renewed prevention efforts, especially vaccination, we are definitely at risk of a resurgence — in fact, a substantial risk of resurgence — of mpox,” Daskalakis said. “This is especially a concern as we approach summer, with the planned and joyous gatherings that may, however, have high potential for skin-to-skin contact, or that are associated with increased sexual activity.” 

He said that at this time those who have already gotten two shots already don't need any more.

There have been more than 30,000 domestic cases of the virus and more than 1.2 million doses of the vaccine have been administered, Braden said: Less than a quarter of the population at risk has been fully vaccinated.

“The mpox outbreak occurred with no warning, peaked in August, with about 460 cases a day. Cases declined to about one per day, at this point, but the outbreak is not over,” he said. 

The latest warning comes after a cluster of 21 cases in Chicago were reported from late April and early May; many of those infected had been previously been vaccinated, and at least one had previously been infected. But, Daskalakis said, those cases were mild, with limited rectal symptoms and fewer lesions.

The origin of last year’s outbreak is believed to be sex at rave parties in Spain and Belgium.

Late last year, "mpox" became the new name for monkeypox. The change, the CDC explained in November, "will enhance the U.S. response to Mpox by using a less stigmatizing term."

By Matthew Chayes

matthew.chayes@newsday.comchayesmatthew

Matthew Chayes, a Newsday reporter since 2007, covers New York City.