Rare Mpox Strain Detected In San Francisco
- Health officials report a rare mpox strain has been detected for the first time in San Francisco. - Mpox cases are rising across California and authorities are urging vaccination to limit further spread. - Officials warn quick action needed to protect vulnerable groups and recommend vaccination clinics; more at (patch.com).
San Francisco has identified its first case of clade I mpox, a rarer strain, in a city resident confirmed on April 14. (sf.gov) The San Francisco Department of Public Health said the patient is an unvaccinated adult who was hospitalized, is improving, and reported close contact with someone who had traveled internationally. (sf.gov) California health officials said April 17 that this was the seventh identified clade I case in California since November 2024 and the first detected in San Francisco. They said investigators are doing contact tracing and enhanced surveillance to look for additional cases. (cdph.ca.gov) Mpox is a viral disease that usually spreads through close, sustained physical contact. The strain that drove the 2022 outbreak in the United States was clade II; clade I is a different branch of the virus that has also produced travel-linked cases in the United States. (cdc.gov) The Centers for Disease Control and Prevention says both clades are spread, treated, and prevented in similar ways, and both can cause fever, swollen lymph nodes, fatigue, and a rash that looks like pimples or blisters. (cdc.gov; sf.gov) State officials are warning now because California’s more common clade II infections are rising again. So far in 2026, the state is averaging 14.5 clade II cases a week, up from 5.8 in 2024 and 3.4 in 2025. (cdph.ca.gov) The Centers for Disease Control and Prevention said the majority of U.S. mpox cases are still clade II and continue to occur in people who are unvaccinated or have received only one dose of JYNNEOS, the two-dose vaccine used against mpox. (cdc.gov) San Francisco and California officials say the immediate risk to the general public remains low, but they are urging people at higher risk to get both vaccine doses before summer travel and large events. (sf.gov; cdph.ca.gov) Health officials are also telling anyone with a new rash that looks like mpox to contact a healthcare provider for testing and to notify partners so they can take steps to prevent further spread. (sf.gov) For San Francisco, the new case does not mark a broad outbreak on its own. It does put the city back into the same mpox response playbook public health agencies have used since 2022: test quickly, trace contacts, and vaccinate people most likely to be exposed. (sf.gov; cdc.gov)
