New Mpox Strain Hits US: Clade I Sparks Health Alert

San Francisco has identified its first case of the more virulent Clade I mpox strain, a development that follows a concerning rise in mpox cases across the United States over the past two years. The confirmed patient, an unvaccinated adult, has since recovered. This marks a significant shift, as Clade I mpox has also been detected in other California cities and New York City, indicating it is no longer solely an imported concern.

Clade I mpox presents a greater health risk due to its higher historical fatality rate, potentially reaching up to 10 percent in Africa, though modern medical care in the US is expected to mitigate this. In contrast, the Clade II strain, prevalent during the 2022 outbreak, had a lower mortality rate. Federal officials anticipate further cases in both Europe and the US, urging vigilance.

Experts note that mpox, regardless of strain, spreads through close skin-to-skin contact, including sexual activity, hugging, and sharing bedding. While animal-to-human transmission is possible, it is not driving the current US outbreak. The CDC advises that the risk to the general population remains low, but the moderate risk to men who have sex with men warrants attention.

Vaccination with the two-dose JYNNEOS vaccine is encouraged for individuals at high risk, including men who have sex with men, and for travelers planning to visit areas with active Clade I mpox outbreaks. Public health departments are actively monitoring the spread and advising proactive measures to control transmission.