California urges mpox vaccination after more-severe strain detected in San Francisco
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California health officials are urging high-risk residents to get vaccinated against mpox after a potentially more-severe strain of the virus was detected for the first time in San Francisco.The strain in question, known as Clade I, was identified in a San Francisco resident and announced by local health officials this week.
The case occurred in an unvaccinated adult who had close contact with someone who had traveled internationally, the San Francisco Department of Public Health said.It was the seventh Clade I mpox case in California, and the resident needed to be hospitalized for treatment.
Clade I was detected for the first time in California in November 2024, in San Mateo County, and additional cases were identified in Los Angeles County in October.Another case of Clade I was identified in L.A.County in January, but there was no further documented spread of the disease, according to the L.A.
County Department of Public Health.California It’s the first time this particular type of mpox, known as “Clade I,” has been found in the United States among people who had no history of traveling overseas to high-risk areas.Most cases of mpox, formerly known as monkeypox, that began spreading in California and the U.S.
in 2022 have been the Clade II strain.Clade I infections are potentially more concerning than Clade II because they may cause more severe illness and spread more easily, such as through close personal contact like sex, massage or cuddling, health officials say.
While Clade I cases remain rare, California officials say Clade II cases are on the rise — with case rates well above those seen in the last two years.So far this year, there have been 14.5 cases of mpox per week, compared with a rate of 3.4 over the comparable time period in 2025 and 5.8 for the comparable time period in 2024.
Most of the people who were infected had not been vaccinated.The vaccine lo...