The CDC’s new alert for doctors and health authorities comes ahead of new vaccine effectiveness data expected to be released by the agency.

It also follows a cluster of infections in the Chicago area from mpox, formerly called monkeypox, many in fully vaccinated residents. While none were hospitalized, potentially thanks to their two doses, authorities are now investigating a range of potential explanations for the breakthrough cases.

“Spring and summer season in 2023 could lead to a resurgence of mpox as people gather for festivals and other events,” the CDC said in the alert, echoing an earlier prediction by the agency´s modelers.

At least 36 new mpox cases have been diagnosed over the past month nationwide, according to figures released by the CDC last week. This includes infections during the days leading up to April 26, which officials had previously heralded as a record week of no new infections.

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

A nationwide vaccination campaign was conducted during 2022 in response to the mpox outbreak that started to rebound in May.

To date, over 1.2 million doses have been administered in the United States, and while there is no specific vaccine for mpox, supplies of smallpox vaccine were used as the two viruses are closely related.

Over 30,000 cases have been reported since past year, while the public health emergency for mpox expired at the end of January.

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