Mpox Cases Surge in SF, Rare Strain Detected

San Francisco has confirmed its first clade I mpox case as California reports a sharp statewide rise in mpox infections. (sf.gov) The San Francisco Department of Public Health said April 16 that the case was confirmed April 14 in an unvaccinated adult who was hospitalized and is now improving. The person 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 the state since November 2024 and that investigators are doing contact tracing and enhanced surveillance. (cdph.ca.gov) Mpox is a virus that usually spreads through close skin-to-skin contact, including sex, and it can start with fever, swollen lymph nodes or fatigue before a rash that looks like pimples or blisters. San Francisco officials said both clade I and clade II spread this way in the United States. (sf.gov) Clade II caused the 2022 U.S. outbreak, but clade I is the newer strain drawing attention now. The Centers for Disease Control and Prevention says clade I risk to most people in the United States remains low, while clade II continues to spread at low levels. (cdc.gov) California’s current increase is mostly in clade II cases. The state said 2026 is averaging 14.5 weekly clade II cases, up from 5.8 in 2024 and 3.4 in 2025, with most infections occurring in people who were unvaccinated. (cdph.ca.gov) San Francisco’s health alert said the city has recorded 1,066 clade II mpox cases since the 2022 outbreak, as of April 9, 2026. The same alert said clade I outbreaks have been ongoing in Central and Eastern Africa since 2023, with more locally acquired cases now being reported in Europe. (sf.gov) The Centers for Disease Control and Prevention says 11 clade I cases were reported in the United States from November 2024 through February 2026, with five more reported since March 2026. The agency said those more recent cases were not linked to one another. (cdc.gov) San Francisco and California officials are urging people at higher risk to get both doses of the Jynneos vaccine, which they said protects against clade I and clade II and lowers the risk of severe illness, hospitalization and death. (sf.gov, cdph.ca.gov) City officials said the exposure risk remains low for people who are not in higher-risk groups, but they want vaccination completed before summer travel and large events. In San Francisco, vaccine access is available through health care providers, pharmacies and city-listed sites for uninsured residents. (sf.gov)