Rare Mpox Strain Detected In San Francisco
- Health officials reported an unusual mpox strain detected in San Francisco amid a statewide rise in mpox cases. - Authorities urged vaccination and surveillance after the first city detection to curb further community spread. - Public-health leaders emphasized expanding vaccination access, testing, and outreach to affected communities to control spread (patch.com).
San Francisco has confirmed its first clade I mpox case, a rarer strain that California says can cause more severe illness than the type tied to the 2022 outbreak. (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 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 the first in San Francisco. The state said health teams are doing enhanced surveillance and contact tracing to look for additional cases. (cdph.ca.gov) Mpox is a virus that spreads mainly through close contact, and the two clades are like two branches of the same virus family. The United States outbreak that began in 2022 was driven by clade II, while clade I has been linked to outbreaks in Central and Eastern Africa and to travel-associated cases outside that region. (cdc.gov, cdc.gov, sf.gov) San Francisco officials said clade II never fully disappeared locally: the city has recorded 1,066 mpox cases since 2022, and 24 residents were diagnosed from January through March 2026. In prior years, the city usually saw fewer than 10 cases in the first quarter. (sf.gov) Statewide, California said clade II cases are running more than twice the average weekly pace of recent years, at 14.5 cases a week in 2026 versus 5.8 in 2024 and 3.4 in 2025. Most of those infections have been in people who were unvaccinated, according to the state. (cdph.ca.gov) Health officials are pushing the JYNNEOS vaccine because they say it protects against both clade I and clade II. San Francisco and California are urging people at risk to get both doses, which are given 28 days apart. (sf.gov, cdc.gov) Symptoms can start with fever, chills, swollen lymph nodes, exhaustion, headache, or cough, followed by a rash that can look like pimples or blisters. The Centers for Disease Control and Prevention says people can spread mpox from the start of symptoms until the rash has fully healed and a fresh layer of skin has formed. (cdc.gov, sf.gov) San Francisco officials said the current exposure risk remains low for people who are not in higher-risk groups, but they want vaccination completed before summer travel and large events. The city is directing residents to health providers, pharmacies, and its mpox information page for vaccine access and testing guidance. (sf.gov, cdph.ca.gov)
