TUESDAY, May 16, 2023 (HealthDay News) -- Public health officials are urging people at risk for contracting mpox to get vaccinated, as they are concerned that a slowdown in infections since last summer may not continue.

In an official update posted Monday on its Health Alert Network, the U.S. Centers for Disease Control and Prevention warned: "Spring and summer season in 2023 could lead to a resurgence of mpox as people gather for festivals and other events."

The CDC is investigating a cluster of mpox cases in the Chicago area. It included 12 confirmed cases and one probable case. All involved men between the ages of 24 and 46 years. Among the 13 cases, nine had received the two-dose Jynneos vaccine. Four had traveled recently to New York City, New Orleans, and Mexico.

Previous outbreaks were mostly related to international travel, but the virus spread rapidly across the world last spring through person-to-person contact. Cases disproportionately affected gay and bisexual men and transgender people, according to the CDC. The outbreak prompted a campaign for people at risk to get vaccinated. Despite breakthrough cases, vaccination can reduce infection severity, the CDC said.

Symptoms of the virus include a blister-like rash, fever, chills, swollen lymph nodes, aches, and fatigue. It can be fatal for those with weakened immune systems.

The World Health Organization last week declared that mpox was no longer a global health emergency, but that does not mean the work is over, said WHO Director-General Tedros Adhanom Ghebreyesus. The disease continues to affect communities in all regions, he said.