New, More Dangerous Mpox Strain Found in 3 Californians

Key Takeaways

Three California residents were infected with Clade 1 mpox, a more severe strain of the disease

The cases mark the first known local spread of this strain in the U.S.

All patients were hospitalized and are now recovering at home in isolation

MONDAY, Oct. 20, 2025 (HealthDay News) — A more dangerous strain of mpox , a virus that causes painful lesions and flulike symptoms, has been detected in three California residents who had not traveled internationally.

Officials said this is the first known local spread of the severe form in the United States.

The strain, called Clade 1, has caused tens of thousands of infections and hundreds of deaths in central and eastern Africa. Until now, it had never spread from person to person inside the U.S., The New York Times reported