The Centers for Disease Control and Prevention (CDC) has issued a warning about the potential spread of a deadlier strain of mpox (formerly known as monkeypox) from Africa to the United States. In a newly released report, CDC officials state that the Democratic Republic of the Congo (DRC) is experiencing its largest-ever mpox outbreak, with cases reaching an all-time high from 2023 to 2024.

The outbreak is primarily driven by a more severe form of mpox called clade I, which has never been detected outside of endemic African regions. Clade I has a significantly higher fatality rate compared to the less severe clade II strain that spread to the US and UK in 2022. According to the CDC, outbreaks of clade I have killed up to 10 percent of infected people, while clade II has a survival rate of 99.9 percent.

The CDC's report analyzed data from DRC's national infectious disease surveillance system, revealing 19,919 cases of clade I mpox and 975 deaths between January 1, 2023, and April 14, 2024. Roughly 67 percent of infections were in patients under 15 years old, accounting for 78 percent of deaths. Cases were reported from 25 out of 26 DRC provinces, including the capital city of Kinshasa for the first time.

Dr. Jono Mermin, director of the CDC's National Center for HIV, Viral Hepatitis, STD, and TB Prevention division, urged Americans most vulnerable to mpox to get vaccinated before the virus potentially returns to the US. "Two doses of the #mpox vaccine is safe & protects from severe illness," he wrote on X (formerly Twitter).

The CDC researchers noted that cases could result from contact with multiple types of infected animals, and communicable spread to close contacts within households likely contributes substantially to the case count. They also suggested that varying demographics across provinces, such as sexual preference, could result in a complex epidemiologic picture.

Mpox is spread through skin-to-skin contact with an infected person, contact with bodily fluids, intimate sexual contact, or contact with infected animals. In 2022, clade II mpox sparked alarm among US health officials when it began to spread rapidly among gay and bisexual men, reaching a peak of 450 cases a day in August. However, infections tapered off amid boosted awareness and a hurried vaccination program, with a total of 32,063 cases and 58 deaths in the US.

The CDC has been working with the DRC to help contain the virus while bolstering preparedness in the United States should clade I emerge among Americans. The agency issued a Health Alert Network notice in December 2023, urging US clinicians to consider clade I mpox infection in persons with mpox signs and symptoms who had recently been in DRC.

Despite the efforts to contain the outbreak, reports of increased mpox cases in some DRC-bordering countries have heightened fears of another, more deadly global outbreak. The CDC team emphasized the importance of vaccinating at-risk individuals, noting that only 23% of persons at risk for clade II mpox infection in the US have completed the two-dose Jynneos vaccination series.

As the world prepares to celebrate Pride Month in June, the news of the lethal mpox strain spreading in Africa has raised concerns among health officials. The CDC has stressed the need for coordinated, urgent global action to support DRC's efforts to contain the virus and prevent its spread to other countries, including the US.