- Clade I Strain Emergence: The US is dealing with the Clade I strain of Mpox, which has a significantly higher fatality rate (1% to 10%) than the common Clade II strain.
- Local Transmission Confirmed: Cases of the severe Clade I variant are now being locally acquired in the US, with Los Angeles confirming infections in individuals with no travel history.
- Key Hotspot States: California, New York, and Washington are currently bearing the brunt of the outbreak, with Los Angeles being a major focus of rising case numbers.
- Primary Containment Strategy: The response relies heavily on the JYNNEOS vaccination rollout for high-risk communities, alongside enhanced surveillance and public awareness efforts.
The United States is experiencing a concerning resurgence of Mpox (monkeypox) cases in 2025, marked by the spread of the more severe Clade I strain. This variant carries a higher fatality rate, ranging from 1% to 10%, compared to the Clade II variant, which is typically below 4%. Los Angeles has recently joined California, New York, and Washington in reporting cases of this more aggressive strain, signifying a concerning shift in the outbreak dynamics.
Health officials are particularly alarmed by the confirmation of locally acquired Clade I cases in Los Angeles County among individuals with no international travel history. This suggests the virus is now circulating within local communities, making containment efforts more complex and urgent than when infections were primarily travel-related. California, in particular, has seen a rapid evolution of the situation since the discovery of these non-travel-linked cases.
States like New York have reported significant case counts, while Washington state has observed a steady rise, particularly within specific high-risk communities. The detection of the virus in wastewater samples in areas like Pierce County, Washington, further indicates potential undiagnosed cases and the need for heightened surveillance. Other states, including New Hampshire, have also confirmed Clade I cases linked to travel.
The core public health response relies on three primary strategies: vaccination campaigns utilizing the JYNNEOS vaccine for high-risk populations, increased surveillance and data collection (including wastewater monitoring), and targeted public awareness campaigns to promote vigilance and early medical attention for symptoms. The coming months are considered crucial in determining whether these proactive measures can successfully contain the Clade I outbreak and prevent a wider epidemic.
