Rare Mpox Strain Detected In San Francisco
- Public health officials reported a rare mpox strain detected in San Francisco as cases rise across California. - Officials urge vaccination amid rising case counts and first local detection of this strain. - The detection could affect control measures and vaccine outreach in the city (patch.com).
San Francisco confirmed its first clade I mpox case on April 14, in an unvaccinated adult who was hospitalized and is improving. (sf.gov) The San Francisco Department of Public Health said the patient had close contact with someone who traveled internationally to an area where clade I mpox is circulating. City officials said exposure risk remains low for people outside higher-risk groups. (sf.gov) California health officials issued a statewide vaccination push on April 17 as mpox cases climbed. The California Department of Public Health said this was the seventh identified clade I case in California since November 2024 and the first in San Francisco. (cdph.ca.gov) Mpox is a virus that usually spreads through close skin-to-skin contact, including sex, and it can cause fever, swollen lymph nodes, fatigue and a blister-like rash. The vaccine used in California, JYNNEOS, is given in two doses 28 days apart and protects against both clade I and clade II. (sf.gov; sf.gov) The strain behind the 2022 U.S. outbreak was clade II, which still circulates at low levels. San Francisco had recorded 1,066 clade II cases as of April 9, 2026, and 24 city residents were diagnosed from January through March this year, compared with fewer than 10 in the first quarter of prior years. (sf.gov) State data shows the broader uptick is not limited to San Francisco. California is averaging 14.5 clade II cases a week in 2026, up from 5.8 in 2024 and 3.4 in 2025, and the state said most recent infections have been in unvaccinated people. (cdph.ca.gov) Clade I has driven a separate outbreak in Central and Eastern Africa since 2023, with more than 53,000 reported cases globally. The Centers for Disease Control and Prevention said the United States had logged 16 clade I cases as of April 17, and most were tied to travel or contact with travelers. (cdc.gov; kqed.org) Federal officials said the risk to most people in the United States remains low, but they expect additional cases in Europe and the U.S. San Francisco and California health officials are responding with contact tracing, surveillance and renewed vaccine outreach before summer travel and large events. (cdc.gov; cdph.ca.gov)
