Mpox could surge again this summer, CDC warns doctors

photo of a labeled vial of the jynneos mpox and smallpox vaccine on a metal tray next to a syringe with a protective cap over its tip
The U.S. may see an uptick in mpox cases this spring and summer. (Image credit: Paul Bersebach/MediaNews Group/Orange County Register via Getty Images)

The United States could see a resurgence of mpox in the coming months, on the heels of spring and summer gatherings, the Centers for Disease Control and Prevention (CDC) cautioned in a health alert released Monday (May 15).

About this time last year, mpox (previously called monkeypox) cases cropped up in dozens of countries where the infection hadn't historically spread. This prompted the World Health Organization to declare the global outbreak a "public health emergency of international concern."  

U.S. mpox rates peaked in August 2022 and declined thereafter, "but the outbreak is not over," the CDC warned in the alert.

The CDC "continues to receive reports of cases that reflect ongoing community transmission in the United States and internationally," the alert reads. For example, the agency is currently investigating a cluster of 12 confirmed mpox cases and one probable case detected in Chicago between mid-April and early May 2023. All of the cases affected men ages 24 to 46, four of whom were confirmed to have recently traveled either domestically or internationally. All of the patients developed symptoms of mpox, but none have been hospitalized. 

Related: Mpox (monkeypox): Symptoms, pictures, treatments & vaccines 

Nine of the 13 Chicago patients had received two doses of the JYNNEOS vaccine, a shot approved for both smallpox and mpox. A person is considered fully vaccinated after two doses of the vaccine. Data collected prior to the ongoing outbreak suggest that two JYNNEOS doses are at least 85% effective at preventing mpox infection, but how long this protection lasts is "currently unknown," according to the CDC

However, even if a vaccinated person has a breakthrough infection, those who are fully vaccinated "may experience less severe symptoms than those who have not" received two doses of the vaccine, according to the alert.

From the start of the global outbreak in May 2022 to May 10, 2023, 30,395 total mpox cases have been reported in the U.S. The outbreak has affected primarily gay and bisexual men and other men who have sex with men, as well as transgender people. That's not because a person's sexual orientation or gender identity makes them more or less prone to infection. Rather, infectious diseases tend to ripple through social networks, and mpox primarily spreads through close physical contact, making it less likely to jump between social networks and spark a more widespread outbreak as a more-transmissible disease like COVID-19 might.  

"To help prevent a renewed [mpox] outbreak during the spring and summer months, CDC is urging clinicians to be on alert for new cases of mpox and to encourage vaccination for people at risk," the alert says. "If mpox is suspected, test even if the patient was previously vaccinated or had mpox. Clinicians should also refamiliarize themselves with mpox symptoms, specimen collection, laboratory testing procedures, and treatment options." 

The CDC does not currently recommend mpox vaccination for the general public, but the agency's alert does include a list of groups considered at high risk for mpox exposure. Doctors should offer mpox vaccination to people in these groups, the agency states. 

People at risk of mpox exposure and those who previously received only one dose of JYNNEOS can search for mpox vaccination sites on the CDC website

Nicoletta Lanese
Channel Editor, Health

Nicoletta Lanese is the health channel editor at Live Science and was previously a news editor and staff writer at the site. She holds a graduate certificate in science communication from UC Santa Cruz and degrees in neuroscience and dance from the University of Florida. Her work has appeared in The Scientist, Science News, the Mercury News, Mongabay and Stanford Medicine Magazine, among other outlets. Based in NYC, she also remains heavily involved in dance and performs in local choreographers' work.