Rare Mpox Strain Detected In San Francisco
- Health officials say mpox cases are rising in California, and a rare strain was confirmed in San Francisco. - This is the first detection of the rare strain in San Francisco, prompting vaccination and testing advisories. - Officials urge eligible residents to get vaccinated to curb spread; more public-health guidance follows (patch.com).
San Francisco has confirmed its first case of clade I mpox, a rarer strain that officials say may cause more severe illness. (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 improving. The patient reported close contact with someone who had traveled internationally to an area where clade I mpox is circulating. (sf.gov) Mpox spreads mainly through close physical contact, including skin-to-skin contact, kissing, sex, and contact with contaminated materials such as bedding or towels. The federal Centers for Disease Control and Prevention says the risk to most people in the United States remains low. (cdc.gov) The strain behind the 2022 outbreak was clade II, while clade I has been linked to more severe disease in some outbreaks. San Francisco health officials said the vaccine used in the United States protects against both clade I and clade II. (cdc.gov, sf.gov) California issued a statewide advisory on April 17 urging people at higher risk to get both doses of the mpox vaccine as cases increase. The California Department of Public Health said most recent California cases have been clade II, not clade I. (cdph.ca.gov) State health officials said California is averaging 14.5 reported mpox cases a week in 2026, up from 3.4 a week in 2025 and 5.8 a week in 2024. They also said most current cases are in people who have not been vaccinated or have received only one dose. (cdph.ca.gov) The state’s vaccine guidance targets gay, bisexual, and other men who have sex with men, transgender people, sex workers, people with multiple sexual partners, and laboratory workers handling orthopoxviruses. The advisory also says people with HIV or other causes of immune suppression can face worse outcomes if they get mpox. (cdph.ca.gov) Nationally, the Centers for Disease Control and Prevention said the United States had reported 11 clade I cases from November 2024 through February 2026, then five more cases since March 2026. The agency said those newer cases were not linked to one another. (cdc.gov) San Francisco officials said people with a new rash, fever, swollen lymph nodes, or rectal pain should seek testing and avoid close contact until they are evaluated. For now, the city says exposure risk remains low for people outside higher-risk groups, but it is pushing vaccination to keep this first clade I case from becoming a wider chain of spread. (sf.gov, sf.gov)
