Clade I Mpox Detected in Riverside County Resident, Public Health Officials Recommend Vaccination Before International Travel

Clade I Mpox Detected in Riverside County Resident, Public Health Officials Recommend Vaccination Before International Travel 

Riverside University Health System Public Health (RUHS-PH) officials identified a travel-associated case of clade I mpox in a Riverside County resident.

The person was no longer contagious at the time they returned to Riverside County after traveling to the Middle East. The individual is at home and has fully recovered.

This is the second case of clade I mpox to be confirmed in California and the sixth case nationwide.

“Travel is often a time of connection, exploration and community. If you may engage in intimate contact while traveling, getting vaccinated against mpox is a simple and effective way to protect yourself and others. If you develop a rash or get sick after international travel, it’s important that you talk to your healthcare provider,” said Dr. Jennifer Chevinsky, Riverside County Public Health Officer.

Mpox is a viral disease that is caused by two virus types, called clades. Clade I is responsible for the current rise of cases in Central and Eastern Africa, while clade II is connected to the broader spread of mpox in Riverside County in 2022. Historically, clade I caused higher numbers of severe illnesses than clade II, though recent outbreaks have seen much lower severity.

Symptoms of clade I and II mpox are similar, and can include fever, rash, swollen lymph nodes, headache and malaise that typically present five to 21 days after exposure. It is primarily spread through close, prolonged contact with a person infected by the virus, or contaminated materials such as bedding or clothing.

Dr. Carlos Calderon, RUHS-PH HIV/STD Medical Director, advises open communication with intimate partners about recent international travel, illnesses or rashes: "It is important to speak candidly with sexual partners and use strategies that reduce the risk of disease.”

In 2025, nine mpox cases, including the clade I case, have been reported in Riverside County, a sharp decrease from the 316 cases reported in 2022. While there have been recent increases in clade II reported in Northern California, Riverside County has not experienced similar increases. Mpox case counts in Riverside County remain low in 2025, but vigilance and vaccination remain essential to prevent further spread.

Riverside County has accounted for approximately 5.3% of all cumulative mpox cases in California while administering roughly 6.2% of the state's total mpox vaccine doses — demonstrating a proactive effort in vaccination outreach and prevention in partnership with healthcare partners, community-based organizations and the broader community.

CDPH has recently updated its mpox vaccination recommendations.  Vaccination with the first dose is recommended at least six weeks prior to travel to areas with ongoing mpox outbreaks, with a second dose to follow four weeks after the initial dose (two weeks before departure) for optimal protection. The vaccine has shown protection for both clade I and clade II mpox. For individuals who have already had two doses, no additional doses are recommended at this time.

For RUHS-PH vaccination clinic locations, visit https://www.ruhealth.org/upcoming-vaccine-clinics or for additional options, visit  EmpoweredAgainstMpox.com.

For more information about mpox in Riverside County, visit www.ruhealth.org/mpox.

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