Rare Mpox Strain Detected In San Francisco
- Health officials report a sharp rise in mpox cases statewide, with a rare strain detected in San Francisco for the first time. - Officials are urging vaccination to curb spread as cases climb and public health monitors investigate transmission patterns. - The detection raises concerns about variant spread and may prompt targeted outreach and vaccine campaigns in affected communities (patch.com).
San Francisco has confirmed its first case of clade I mpox, a rarer strain that California says is appearing as mpox cases rise statewide. (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 mpox case in the state since November 2024 and the first in San Francisco. The state said public health teams are doing enhanced surveillance and contact tracing to look for additional cases. (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 the exposure risk remains low for people outside higher-risk groups. (sf.gov) The strain behind the 2022 U.S. outbreak was clade II, not clade I. San Francisco health officials said clade II has led to 1,066 cases in the city as of April 9, 2026, and it is still circulating in California. (sf.gov) California said it is averaging 14.5 clade II cases a week in 2026, up from 5.8 in 2024 and 3.4 in 2025. The state said most of those recent infections have been in people who were unvaccinated. (cdph.ca.gov) Federal health officials say the risk from clade I mpox to most people in the United States remains low. The Centers for Disease Control and Prevention said there were 11 reported U.S. clade I cases from November 2024 through February 2026, plus five more reported since March 2026. (cdc.gov) San Francisco and California are urging people at risk to get both doses of the Jynneos vaccine, which officials say protects against both clade I and clade II. The city said doses are available through health care providers, pharmacies and local public health sites. (sf.gov) For now, officials are treating the San Francisco case as travel-linked, not evidence of broad local spread. Their next step is the same as their first: find contacts, watch for more cases and push vaccination before summer travel and large events. (cdph.ca.gov)
