CDC investigates possible mpox resurgence after report of Chicago cluster

The Centers for Disease Control and Prevention (CDC) is looking into a potential cluster of mpox cases reported in the Chicago area, with many of the reported cases occurring among individuals who were vaccinated.

“A cluster of mpox cases have been reported in the Chicago area, which means the virus is still spreading, and we need to continue to be alert. More than 50% of cases in the cluster have been in people who have been previously vaccinated,” the CDC said in a statement on Wednesday.

The agency said it does not know why this cluster of people got infected after vaccination, whether the virus has changed or if immunity decreased. The CDC noted that no vaccine is 100 percent effective at preventing infection.

Officials are conducting studies into how long immunity lasts following vaccination and are also looking into how the virus spread among the Chicago area patients.

The virus, spread through skin-to-skin contact, causes flu-like symptoms as well as its characteristic skin lesions.

A nationwide vaccination campaign was carried out during 2022 in response to the mpox outbreak that began picking up in May. More than 1.2 million doses have been administered in the U.S. While there is no vaccine specifically for mpox, federal officials deployed supplies of smallpox vaccines as the two viruses are closely related.

Amid the outbreak, federal officials turned to administering two one-fifth doses of the Jynneos smallpox vaccine intradermally in order to stretch supply. The CDC on Wednesday said, “It’s never too late to get the second dose.”

More than 30,000 cases have been linked to the outbreak that started last year, though the public health emergency for mpox expired at the end of January. The current seven-day average for cases in the U.S. is one.

The relatively quick handling of the mpox campaign was largely attributed to changes in behavior among men who have sex with men, the demographic through which the mpox various predominantly spread in 2022.

The CDC did not disclose whether these recent infections occurred among men who have sex with men, and public health experts have stressed that mpox does not discriminate.