A recent spike in mpox diagnoses in Chicago, some of them in people vaccinated against the virus, raised concerns about a possible surge in cases among gay and bisexual men over the summer.

On Monday, Howard Brown Health, an LGBTQ-focused clinic in Chicago, reported eight new cases of mpox, formerly known as monkeypox, since April 17. By comparison, only one case, also diagnosed in Howard Brown, was reported to the Chicago Public Health Department in the previous three months.

Public health experts expressed moderate concern that, like other cases of infections that are transmitted through sexual contact, mpox cases could increase during the summer, especially when gay and bisexual men travel to festivals in the Pride and other major LGBTQ events.

“Without renewed vaccination and prevention efforts, we risk a resurgence of mpox,” said Dr. Demetre Daskalakis, White House deputy coordinator of the national mpox response. «The vaccine is a really important tool, even if it’s not perfect.»

Diagnosed cases have «increased slightly» in eight countries in the past three weeks, including France and several East Asian countries, said Dr. Rosamund Lewis, technical lead for mpox at the World Health Organization. About half of the recent French cases were in vaccinated people.

Otherwise, global case counts have continued to decline since the peak in early August. Since mid-April, Lewis said, only 21 of the 111 nations that reported cases during the outbreak have reported new diagnoses. However, many cases can go undetected, she said.

Chicago’s weekly mpox case rate is the highest since early November. According Data from the Centers for Disease Control and Preventionwhich is updated biweekly, the US has had a seven-day moving average of no more than 17 diagnoses since mid-February.

The Howard Brown Clinic is analyzing the new cases to determine if any are part of a linked group of infections.

Mpox vaccination rates are insufficient

Seven of the eight newly diagnosed patients were gay or bisexual men, said Dr. Leanna Gordon, medical director of preventive medicine at Howard Brown. One person was not vaccinated, another had received a two-dose Jynneos vaccine, and six were fully vaccinated.

All eight cases were mild and none of them required pain treatment. Even with advanced infection, the vaccine is likely to reduce the severity of an infection, Gordon said.

Gordon stressed the importance of people at substantial risk of mpox receiving both doses of the Jynneos vaccine to protect themselves and their sexual partners.

“One of our main concerns is that our at-risk population is not vaccinated,” Gordon said. “We have not had as much interest in the vaccine as we would like.”

According to the Centers for Disease Control and Prevention, more than 1.2 million doses of the Jynneos vaccine have been administered across the country to 725,000 people, 90% of them men. The agency Dear All that only 1 in 4 of the people most at risk, including gay and bisexual men and transgender people, have been fully vaccinated.

Two doses of Jynneos vaccine reduced the risk of mpox disease by 69%, and that dose was 37% effective, the CDC reported in December. Updated figures are expected next week.

Public health experts expressed concern that mpox could spread more widely across the country after Chicago hosts the International Mr. Leather festival, a popular destination for gay men, later in the month.

Daskalakis said the CDC is working with Howard Brown and other local partners to use the event to promote mpox prevention and awareness.

Dr. Jeffrey Klausner, an infectious disease physician at the University of Southern California, said, «We need to maintain vigilance and promote and provide free vaccination.»

symptoms of mpox

Mpox, which has an incubation period of approximately three to 17 days, usually manifests such as a rash and lesions. Other potential symptoms include:

  • Fever.
  • Shaking chills.
  • Swollen lymph nodes.
  • Exhaustion.
  • Muscle pains.
  • Headache.
  • Sore throat.

In France, the national health authorities recently reported that of the 19 diagnoses this year through April 3 in the Centre-Val de Loire region, 16 were made after March 1 and all but one were in men who have sex with men. Ten of the cases were in people who were fully vaccinated: six who had two doses of Jynneos vaccine and four who had received childhood smallpox vaccine and a recent dose of Jynneos.

Could mpox come back this summer?

last summer mpox outbreak decreased after a combination of vaccination, immunity after infection, and behavior change among gay and bisexual men.

Infectious disease experts believe that existing immunity from previous infections and vaccinations would likely prevent mpox from spreading at the same level as last year.

But questions remain about the duration of immunity and whether gay men, many of whom reported reducing their number of sexual partners or even practicing abstinence last summer, have returned to their basic behavior patterns after mpox cases dropped dramatically.

“Everyone’s efforts have helped control the outbreak, but it hasn’t gone away,” Lewis said. she noticed that there is evidence that mpox can be spread both before symptoms start and from people who never develop symptoms.

Dr. Marc C. Shamier, a clinical microbiology resident at the University Medical Center Rotterdam in the Netherlands, reported that in September about 45% of gay and bisexual men visiting sexual health centers in Rotterdam and Amsterdam they had detectable antibodies against orthopoxviruses, the family to which mpox belongs.

«However,» Shamier said in an email, «this level of immunity is not sufficient to completely stop viral circulation, so sporadic clusters of monkeypox are to be expected.»

Shamier continued: «Large-scale events, such as the annual Pride parties, could increase the number of sexual contacts among the risk group, which can lead to an increase in viral circulation and infections.»

With testing, case isolation, and higher levels of mpox immunity among risk groups, Shamier expects the number of cases to be relatively low compared to last year.

Daskalakis said the recent cases in Chicago amount to «a call to action rather than a call to panic.»

“We have the tools to take care of this,” he said. «We just have to do it.»