Rare Mpox Strain Detected In San Francisco

San Francisco has confirmed its first clade I mpox case, a rarer strain that California officials say triggered a statewide vaccination push. (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. (sf.gov) California’s health department said April 18 that mpox cases are rising statewide and urged people at higher risk to get both doses of the Jynneos vaccine. The agency said the vaccine protects against both clade I and clade II mpox. (cdph.ca.gov) Mpox is a viral disease that usually spreads through close physical contact, including sex, kissing, cuddling, and sharing bedding, towels, or clothing. Common symptoms include a rash, fever, swollen lymph nodes, chills, exhaustion, and muscle aches. (cdc.gov) Clade I and clade II are two genetic branches of the virus, similar to two family lines of the same disease. The Centers for Disease Control and Prevention said clade I has been linked to outbreaks in central and eastern Africa and is being watched because it may cause more severe illness in some settings. (cdc.gov) San Francisco officials said the risk to the general public remains low, but they warned that local clade II cases are already running ahead of recent years. The city recorded 24 clade II cases from January through March 2026, compared with fewer than 10 in the first quarter of prior years. (sf.gov) Statewide data show the longer-term outbreak never fully disappeared in California. The California Department of Public Health said mpox has circulated in the state since 2022 and continues to be tracked through case reports and wastewater surveillance. (cdph.ca.gov) Nationally, the Centers for Disease Control and Prevention said 11 clade I cases were reported in the United States from November 2024 through February 2026, with five additional cases reported since March 2026. The agency said those March cases were not linked to one another. (cdc.gov) Health officials are telling people with a new unexplained rash or other mpox symptoms to avoid close contact and seek medical care. In San Francisco, the immediate public health response is focused on vaccination, contact tracing, and watching for any sign that this first clade I case leads to more. (sf.gov)