Rare Mpox Strain Detected In San Francisco
- Health officials report rising mpox cases in California and detected a rare strain in San Francisco. - Officials urge vaccination as cases soar statewide, with the rare strain confirmed for the first time locally. - The detection raises urgency for vaccination and outreach to high-risk communities, officials say (patch.com).
San Francisco has confirmed its first clade I mpox case in a city resident, and California health officials say mpox cases are rising statewide. (sf.gov) The San Francisco Department of Public Health said April 16 that the case was confirmed on April 14 in an unvaccinated adult who was hospitalized and is improving. The person reported close contact with someone who had traveled internationally to an area where clade I mpox is circulating. (sf.gov) California’s public health department said April 17 that this was the state’s seventh identified clade I case since November 2024 and the first in San Francisco. Officials said they are doing enhanced surveillance and contact tracing to look for additional cases. (cdph.ca.gov) Mpox is caused by a virus in two main groups, called clade I and clade II. The 2022 outbreak in the United States and California was driven by clade II, while clade I has been tied to more recent outbreaks in Central and Eastern Africa and some travel-linked cases in Europe and the U.S. (cdc.gov) The Centers for Disease Control and Prevention said April 17 that the risk from the clade I outbreak remains low for most people in the United States. The agency reported 16 U.S. clade I cases from November 2024 through mid-April 2026, including five reported since March 2026. (cdc.gov) California officials said the bigger immediate trend inside the state is a rise in clade II infections, with an average of 14.5 weekly cases in 2026 so far, compared with 5.8 in 2024 and 3.4 in 2025. They said most of those recent infections have occurred in people who were unvaccinated. (cdph.ca.gov) Health officials say both clades spread mainly through close skin-to-skin contact in the United States, including during sexual activity, and both can cause fever, swollen lymph nodes, fatigue, and a rash that looks like pimples or blisters. San Francisco said people with a compatible rash should seek testing and notify partners. (sf.gov) The vaccine being offered in California is intended to protect against both clade I and clade II, and San Francisco and the state are urging people at higher risk to get both doses before summer travel and large events. Officials said the current exposure risk remains low for people outside higher-risk groups. (sf.gov)
