Rare Mpox Strain Detected In San Francisco
- Health officials report a surge in mpox cases statewide and detected a rare strain for the first time in San Francisco. - Officials urge vaccination as cases climb; the rare strain was detected in a local San Francisco patient. - Public-health leaders warn residents to get vaccinated and seek testing after the new detection (patch.com).
San Francisco has confirmed its first clade I mpox case, a rarer strain than the virus behind the city’s 2022 outbreak. (sf.gov) The San Francisco Department of Public Health said the case was confirmed on 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 this was the seventh identified clade I case in the state since November 2024 and the first in San Francisco. They said most U.S. clade I cases have been linked to international travel or close contact with travelers from places where the virus is circulating. (cdph.ca.gov) Mpox is a viral infection 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 appears. San Francisco officials said both clade I and clade II cause similar symptoms, but they are tracking whether clade I leads to more severe illness in the United States. (sf.gov) The 2022 U.S. outbreak was caused by clade II, not clade I, and San Francisco has recorded 1,066 total mpox cases since that outbreak began. A separate clade I outbreak has been underway in Central and Eastern Africa since 2023, with travel-related cases and some local spread reported in Europe. (sf.gov) The city’s warning comes as ordinary clade II mpox is also rising again. San Francisco reported 24 clade II cases from January through March 2026, after recording fewer than 10 cases in the first quarter of prior years. (sf.gov) Statewide, California is averaging 14.5 clade II cases a week in 2026, up from 5.8 in 2024 and 3.4 in 2025. The California Department of Public Health said most of those recent infections were in people who were unvaccinated. (cdph.ca.gov) Health officials are urging people at higher risk to complete the two-dose JYNNEOS vaccine series, which the Centers for Disease Control and Prevention says protects against both mpox and smallpox. The second dose is due 28 days after the first, but the CDC says people who are late should still get it as soon as possible. (cdc.gov) San Francisco officials said exposure risk remains low for people outside higher-risk groups, but they are expanding surveillance and contact tracing around this case. With summer travel and large events approaching, state and city officials are pushing vaccination and testing before another seasonal rise. (cdph.ca.gov)
