Publisher Health

Clinics nationwide will begin offering vaccinations against monkeypox to anyone who may have been exposed to the virus, federal health officials announced on Tuesday.

Until now, immunizations were offered only to people with a known exposure.

States will receive doses of a safer and newer monkeypox vaccine called Jynneos from the federal stockpile, based on the number of cases and the proportion of the state’s population at risk for severe disease, the officials said at a news briefing.

State health authorities may also request supplies of an older vaccine developed for smallpox, which is believed to protect against monkeypox, as well.

The Department of Health and Human services will provide 56,000 doses of the Jynneos vaccine immediately and an additional 240,000 doses in the coming weeks. Another 750,000 doses are expected to become available over the summer, and a total of 1.6 million doses by the end of this year.

“This vaccine currently has some limitations on supply, and for this reason the administration’s current vaccine strategy prioritizes making it available to those who need it most urgently,” Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, said.

The older smallpox vaccine, called ACAM2000, is associated with harsh side effects, including death, in people who are immunocompromised, pregnant women and older adults.

The new vaccination plan drew quick criticism from experts, who said the campaign was too small and slow to make an impact. The longer it takes to contain the monkeypox outbreak, the greater the chances that the virus will become entrenched in the United States, particularly among men who have sex with men, researchers warned.

“Many of us are concerned that the window is closing for us to be able to eliminate monkeypox,” said Dr. Celine Gounder, an infectious disease expert and editor at large for public health at Kaiser Health News.

“If we don’t start vaccinating more quickly and broadly, we’re going to have a very difficult time containing this,” she said. Ideally, tests and vaccines for monkeypox could have been offered at L.G.B.T.Q. Pride events across the country in order to reach men at high risk of contracting the virus, Dr. Gounder added.

Some experts said the plan was also unfair to men at risk who will not have access to the Jynneos vaccine, especially those who have H.I.V. and cannot safely take the older smallpox vaccine.

“There won’t be enough to meet the need,” said Elizabeth Finley, director of communications for the National Coalition of STD Directors. “Plus, without better testing capacity, a strategy based on contacts with a positive case falls flat.”

It’s also not clear what qualifies as a probable exposure, she added: “Do you need to know someone at the event tested positive, or do you just say, ‘Oh, I went to a rave and I want to be safe’?”

Many clinicians are worried about side effects and scarring from the older smallpox vaccine, as well as the misinformation and vaccine hesitancy they might fuel, Ms. Finley said. “We’ve had clinicians say that there’s no way in hell they would give somebody ACAM2000,” she said.

The Jynneos vaccine, on the other hand, has never been used on this scale, and federal health officials said they would watch for unexpected side effects.

The administration has so far provided more than 9,000 doses of Jynneos vaccine and 300 courses of antiviral treatments to 32 jurisdictions in the country, officials said on Tuesday.

The European Union is adopting a similar plan, sending 5,300 of its 100,000 Jynneos doses to Spain, which has the most cases, followed by Portugal, Germany and Belgium. Other member states will receive doses in July and August.

The number of monkeypox cases has risen sharply in many European countries and in the United States.

As of June 28, there were 306 cases in 27 states and the District of Columbia, up from 156 cases a week earlier. The C.D.C. has activated its emergency operations center to better monitor and respond to the outbreak, Dr. Walensky said.

The reported numbers are likely to be underestimates, said Dr. Jay Varma, director of the Cornell Center for Pandemic Prevention and Response. “It’s pretty clear to me and I think many others that the epidemic is far larger in magnitude than what our official case counts suggest it is,” he said.

Given the rising numbers, the available doses are not likely to be enough to meet the demand. Washington’s health department offered 300 monkeypox vaccination appointments on Monday; the slots filled up in less than 15 minutes.

New York City, which had identified 55 cases of monkeypox as of Tuesday, had 1,000 doses of the Jynneos vaccine at hand. The city’s health department began administering the vaccines at a single clinic in Chelsea, where the clientele is largely affluent white men who have sex with men.

The city offered the first doses at noon on June 23. Less than two hours later, officials announced that the clinic could no longer accommodate walk-ins and had booked appointments through June 27. As of Tuesday, the city was still waiting for more vaccine doses to become available.

“It started and then it stopped, and it started without anyone being prepared, and I’m not sure when it’s coming back,” said Keletso Makofane, a social network epidemiologist at the FXB Center for Health and Human Rights at Harvard University.

“All of this uncertainty does not help us to cultivate the trust we need to have,” Dr. Makofane said.

Several experts also took issue with the location and said it would have been more equitable to offer the vaccines at clinics frequented by Black men with untreated H.I.V. and limited access to health care.