New Deadly Strain of Mpox Virus Emerges in California

A new strain of the Mpox virus, identified as Clade I, has been discovered in California, raising concerns about its severity and transmission. Two residents of Los Angeles County tested positive for this strain, which has a fatality rate of up to 10%. Health officials confirmed that both individuals contracted the virus locally, marking the first instance of Clade I being acquired within the United States.

The first case was reported on October 17, 2025, involving a resident from Long Beach, with the second case following shortly thereafter. Both patients were hospitalized but are now recovering at home, according to the Los Angeles County Department of Public Health. Details regarding the patients’ identities have not been disclosed.

Understanding Clade I and Its Implications

Clade I is considered more severe than the currently circulating Clade II, which has a mortality rate of less than 3% and has resulted in the deaths of 63 individuals in the U.S. since the 2022 outbreak. The new strain is noted for its increased transmissibility, which includes spread through close personal contact such as hugging, massages, and sexual intercourse.

The Centers for Disease Control and Prevention (CDC) reported that there have been six previous cases of Clade I in the U.S., all of which involved individuals who had traveled to regions in Central and East Africa, including a case in California in November 2024. Health officials emphasized that these cases were not connected.

Mayor Rex Richardson of Long Beach remarked, “While the overall risk of exposure to the public remains low, we are taking this very seriously. This underscores the importance of continued surveillance, early response, and vaccination.”

Transmission and Symptoms of Mpox

Mpox, formerly known as monkeypox, spreads through intimate contact. According to the Los Angeles County Department of Public Health, the virus can be transmitted through bodily fluids, sores, shared bedding, and even through coughing or sneezing. Symptoms of the disease include unusual rashes or sores resembling pimples or pus-filled blisters on the face, body, and genitals, along with fever, chills, headache, and swollen lymph nodes.

In areas where Mpox outbreaks have been prevalent, such as the Democratic Republic of the Congo (DRC), transmission has often occurred through contact with infected animals and crowded living conditions. Most patients typically recover without severe complications, though antiviral treatments may be considered for those at higher risk.

The Long Beach Department of Health and Human Services has advised the public to avoid intimate contact if experiencing any unexplained rashes or lesions. Those at risk, particularly gay and bisexual men, can access the JYNNEOS vaccine, which is administered in two doses to prevent infection.

Public health officials are closely monitoring the situation as they urge the community to remain vigilant and informed regarding Mpox.