Rare Mpox Strain Detected in San Francisco

San Francisco has confirmed its first clade I mpox case, a strain California officials say can cause more severe illness than the version seen in 2022. (sf.gov) The San Francisco Department of Public Health said April 14 that the patient is an unvaccinated adult who was hospitalized and is improving. The person reported close contact with someone who had traveled internationally to a place where clade I mpox is circulating. (sf.gov) Mpox is a viral disease that usually spreads through close, often skin-to-skin contact, and it can cause a painful rash, fever, and swollen lymph nodes. The Centers for Disease Control and Prevention says the JYNNEOS vaccine is given in two doses, four weeks apart, and people should still get the second dose even if they are late. (cdc.gov) California’s health department said this San Francisco case involved clade I, while most U.S. cases since 2022 have involved clade II. State officials said vaccination protects against both clades and urged people at higher risk to get both doses. (hca.venturacounty.gov) The vaccination push comes as California reports rising mpox activity in 2026. A state advisory said weekly clade II case averages rose to 14.5 in 2026, up from 5.8 in 2024 and 3.4 in 2025, with most recent infections occurring in unvaccinated people. (changeflow.com) San Francisco officials said the exposure risk remains low for people who are not in higher-risk groups. They are asking clinicians to watch for symptoms, ask about travel and close contacts, and test suspected cases quickly. (sf.gov) Clade I has drawn attention because it has been linked to larger outbreaks in central and eastern Africa since 2023. KQED, citing global health data, reported more than 53,000 cases and at least 200 deaths tied to that outbreak. (kqed.org) The Centers for Disease Control and Prevention recommends vaccination for adults at risk during an mpox outbreak, and federal advisers backed routine use of the two-dose JYNNEOS series for those groups in 2024. In San Francisco, officials are using that same message now: the patient was unvaccinated, and the city wants at-risk residents fully vaccinated before more cases appear. (cdc.gov; cdc.gov; sf.gov))