The number of U.S. mpox cases has more than doubled compared with last year, and the federal Centers for Disease Control and Prevention has been urging clinicians across states to encourage vaccinations for those at risk.

As of May 25, the nation had seen a roughly 150% increase in cases of the disease formerly known as monkeypox — from 434 at that time last year to 1,089 this year, according to the CDC . About a third of the cases are in New York state, New York City (which the CDC reports separately), New Jersey and Pennsylvania.

Anyone can contract mpox , a viral disease that can cause a rash, pain severe enough to require hospitalization and — in rare cases , primarily in patients with other complications — death. But during 2022’s U.S. outbreak, the contagious infection mainly affected men in gay and bisexual communities. While it’s not a sexually transmitted infection, mpox can be passed through skin-to-skin contact, respiratory droplets or contact with bodily fluids.

June is Pride Month, and public health experts are concerned about a potentially higher caseload this summer as people gather for large celebrations. Experts are encouraging vaccination outreach, especially to Black and Hispanic LGBTQ+ people, who are less likely to be vaccinated and more likely to face barriers to getting care.

Those who are at highest risk for mpox, including men who have sex with men and people with advanced HIV, should receive two doses, four weeks apart, of the trademarked Jynneos vaccine to prevent infection.

The CDC has warned that low vaccination rates among those groups with the highest risk of mpox exposure could lead to a resurgence of the disease.

Dr. Richard Silvera, an assistant professor of infectious diseases at the Icahn School of Medicine at Mount Sinai in New York City, said the current mpox rates are far lower than they were in 2022, when there were more than 3,800 cases citywide, but that the numbers are growing rapidly.

“I am very concerned that there will be increased rates over the summer, particularly as we hit Pride Month,” Silvera said.

New York City has seen more than 200 cases this year — up from 46 at this time last year. It’s unclear what is causing the surge, but Silvera and other experts say one factor could be that some patients may not have received their second doses.

“Either their immunity is waning, or folks didn’t get complete vaccination,” he said. “And so now there’s been time for that virus to exploit those gaps in protection.”

The New York City Department of Health and Mental Hygiene released an advisory in early May, noting that of the 256 diagnoses between October 2023 and April 15, 73% were among unvaccinated people or people who had received only one dose.

“There’s a large overlap between people who belong to BIPOC communities, living with HIV, identifying as LGBTQ+,” said Preeti Pathela, executive director of the STI program at the agency.

“Our hope is that, through this kind of regular outreach which we have intensified in the last couple of months, knowing that coming into the summer is going to be a critical time to really double down, we’re just hoping that the messaging and the services get out to the communities that need it.”

Racist language associated with the former name of mpox helped spur the World Health Organization to rename it in 2022. Public health experts also were concerned that the former name might be discouraging people from being tested and vaccinated by contributing to the stigma surrounding the disease.

In reports last month, the CDC warned of a heightened global threat of a deadlier strain of mpox that is devastating the Democratic Republic of Congo, where the virus is endemic. That strain hasn’t been detected in the United States, but the agency and clinicians are on alert for possible cases in travelers from the country.

Infectious disease physician Dr. Anu Hazra said he and others in the field are closely watching that strain.

“The only way that we can truly think about eradicating mpox is bringing vaccines to everywhere in the world that’s impacted by the illness,” said Hazra, who sees patients at Howard Brown Health, which runs several clinics in the Chicago area focused on LGBTQ+ care.

HIV patients are at higher risk of contracting mpox, and are disproportionately Black and Hispanic. Racism, homophobia and barriers to care such as poverty and a lack of transportation complicate prevention and treatment efforts.

“When we think about, sort of, any communicable disease, we know that it tracks along racial and economic fault lines. We’ve seen that with HIV, we’ve seen that with COVID, we see that with certain STIs — we have certainly seen it with mpox,” Hazra said.

Silvera, of the Icahn School of Medicine, said clinicians and state health agencies also should consider the historic distrust of medicine among Black and Hispanic communities.

“It takes a lot of time. We’re undoing decades and centuries of work,” he said. “It’s a tough job. And so, we can do that person to person, but it’s also going to require larger efforts as well to undo these disparities.”

Along with distrust and vaccine skepticism, fear of being “outed” as gay is a major barrier in some Black communities, said Ryan Payne, a prevention specialist at the Alliance of AIDS Services-Carolina. The organization serves six counties in North Carolina.

“That is a full-blown truth. It’s very hard. Me and my co-workers are talking about that all the time,” Payne said.

At the end of April, the North Carolina Department of Health and Human Services found that 30 of the 51 cases over the previous six months were among Black people. But only 27% of patients vaccinated in the state this year were Black.

In Pennsylvania, there have been 64 reported mpox cases compared with two at this time last year, according to the CDC. The state’s health department said it will emphasize the importance of vaccinations throughout 2024, using an awareness campaign that will focus on reaching the at-risk populations through social media and dating apps.

Cory Haag, a registered nurse at the Central Outreach Wellness Center in Pittsburgh, said the best way to stem the spread is by addressing barriers, educating patients and quelling fears within the LGBTQ+ community the center serves.

Many patients travel for up to two hours to receive care at the center. It provides bus passes to patients so they can more easily return for a second vaccine dose.

“We’re just happy to be that safe space to catch them,” Haag said.