CDC Alerts Over Potential Mpox Resurgence

As CDC investigates a cluster of mpox cases in the Chicago area, the agency is asking clinicians and public health agencies to be on the lookout for more local outbreaks.

In a Health Action Network update on Monday, the CDC said that while cases of mpox — formerly known as monkeypox — have declined since last summer’s peak, “the outbreak is not over.” Community transmission continues, and the spring and summer season “could lead to a resurgence of mpox as people gather for festivals and other events,” the agency wrote.

The alert was, in part, prompted by 13 cases reported to the Chicago Department of Public Health from April 17 to May 5, with nine (69%) involving individuals fully inoculated with the modified vaccinia Ankara-Bavarian Nordic vaccine (Jynneos).

“Although vaccine-induced immunity is not complete, vaccination continues to be one of the most important prevention measures,” the CDC said, adding that people who have completed their two-dose series “may experience less severe symptoms.”

While all of the Chicago-area cases were symptomatic, none required hospitalization. Nine of the cases occurred in white men, with two cases each in Black and Asian men. In the nine cases where travel history was available, four had recently traveled to places including New Orleans, New York City, and Mexico.

Since the global outbreak began in 2022, more than 30,000 mpox cases have been identified in the U.S., peaking at 460 daily cases in August 2022. A disproportionate number of cases have affected men who have sex with men (MSM).

In recent months, cases have become exceedingly low and mpox has largely fallen out of the public view. The U.S. ended the public health emergency for mpox at the end of January, and the World Health Organization last week said the outbreak no longer represents a global health emergency.

But with spring here and summer approaching, the CDC is urging clinicians to watch for new cases, including in people who were previously vaccinated or infected.

Typical symptoms of mpox include deep-seated, vesicular or pustular lesions, with differential diagnoses including shingles, chickenpox, molluscum contagiosum, scabies, and allergic skin rashes, along with sexually transmitted infections (STIs) such as herpes simplex virus and syphilis. In its alert, the CDC also suggested that clinicians reacquaint themselves with recommended methods for specimen collection and laboratory testing procedures.

In terms of vaccination, at-risk groups eligible for Jynneos include people with a known or suspected mpox exposure, MSM or transgender people who in the past 6 months have had sex with more than one partner or have developed a new STI, sex workers, and people with HIV infection or other immunosuppressive conditions who anticipate potential exposures. Severe mpox cases often have involved people living with HIV.

Patients with an mpox diagnosis may need supportive care and pain control with topical or systemic strategies.

While not approved specifically for mpox, tecovirimat (Tpoxx) is considered a first-line option for treatment, and the CDC suggested that clinicians consider enrolling patients in the STOMP (Study of Tecovirimat for Human Monkeypox Virus) trial, so efficacy of the smallpox drug can be properly evaluated.