Rare Mpox Strain Detected In San Francisco
- Mpox cases are soaring across California, and a rare strain was detected in San Francisco for the first time. - Health officials are urging Californians, especially at-risk groups, to get vaccinated against mpox to curb spread. - State agencies are monitoring cases and urging vaccination to prevent wider outbreaks (patch.com).
San Francisco has confirmed its first clade I mpox case, a rarer strain that health officials say may cause more severe illness than the virus behind the 2022 outbreak. (sf.gov) The case was confirmed April 14 in an unvaccinated adult who was hospitalized and is improving, according to the San Francisco Department of Public Health. The patient reported close contact with someone who had traveled internationally to an area where clade I mpox is circulating. (sf.gov) Mpox spreads mainly through close skin-to-skin contact, including sex, and the rash can look like pimples or blisters after flu-like symptoms such as fever, swollen lymph nodes, or fatigue. San Francisco officials said the vaccine protects against both clade I and clade II mpox. (sf.gov) Clade II is the version that drove the 2022 U.S. outbreak, and San Francisco has recorded 1,066 cases from that outbreak as of April 9, 2026. Clade II never disappeared entirely: 24 San Francisco residents were diagnosed from January through March 2026, compared with fewer than 10 cases in the first quarter of prior years. (sf.gov) California’s statewide mpox dashboard says case data were refreshed April 10, 2026, and the state is still tracking infections from the 2022-era virus. The California Department of Public Health does not break those public totals out by clade on its dashboard. (cdph.ca.gov) Federal officials say clade I remains rare in the United States, but the count has been rising. The Centers for Disease Control and Prevention said April 17 that 11 clade I cases were reported nationally from November 2024 through February 2026, with five more reported since March 2026. (cdc.gov) The strain now showing up in San Francisco is part of a wider outbreak that has spread far beyond Central Africa. The Centers for Disease Control and Prevention said more than 53,000 confirmed clade I cases and more than 150 deaths had been reported globally since January 2024. (cdc.gov) San Francisco health officials said exposure risk is still low for people outside higher-risk groups, but they are urging vaccination for people at risk and for travelers heading to places where clade I has been reported, including parts of Europe and Africa. The JYNNEOS vaccine is given in two doses, 28 days apart. (sf.gov) The city’s guidance is aimed especially at gay, bisexual, and other men who have sex with men, as well as transgender people who have sex with men, because that is where most reported U.S. cases have been concentrated. People who got one dose more than 28 days ago can get the second dose immediately, city officials said. (sf.gov) For now, San Francisco officials say they have not identified broad community spread of clade I in the city. Their message is narrower and more immediate: finish the two-dose vaccine series before summer travel and large events push contact rates higher. (sf.gov)
