Rare Mpox Strain Detected In San Francisco
- Mpox cases are rising across California, with health officials reporting the first local detection of a rare strain in San Francisco. - State and city health departments urged residents to seek vaccination, testing, and watch for symptoms to limit spread. - Officials warned increased vigilance is needed, noting potential clinic outreach and wider vaccination efforts may follow (patch.com).
San Francisco has confirmed its first clade I mpox case, a rarer strain that California health officials say is showing up as statewide cases rise. (sf.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 that looks like pimples or blisters appears. San Francisco’s health department said the case was confirmed April 14 in an unvaccinated adult who was hospitalized and is improving. (sf.gov) There are two main types of the virus, clade I and clade II. The 2022 U.S. outbreak was driven by clade II, while clade I cases in the United States have remained rare and are still being monitored to see whether they cause more severe illness here. (cdc.gov, sf.gov) California said this San Francisco infection is the state’s seventh identified clade I case since November 2024 and the first in the city. State officials said the patient had close contact with someone who had recently traveled internationally to an area where clade I mpox is circulating. (cdph.ca.gov) The state’s broader concern is not just the one rare case. California said it is averaging 14.5 clade II mpox cases a week in 2026, up from 5.8 in 2024 and 3.4 in 2025. (cdph.ca.gov) San Francisco has also seen its local baseline move up. A city health alert said 24 residents were diagnosed with clade II mpox from January through March 2026, compared with fewer than 10 cases in the first quarter of prior years. (sf.gov) Health officials are pushing vaccination because the same vaccine is used against both clades. The Centers for Disease Control and Prevention says JYNNEOS is a two-dose vaccine, and California says two doses can cut the risk of infection while helping prevent severe illness, hospitalization, and death. (cdc.gov, cdph.ca.gov) The groups most affected in the United States have been gay and bisexual men and other men who have sex with men, along with transgender people who have sex with men, according to San Francisco health officials. The city said exposure risk remains low for people who are not in higher-risk groups. (sf.gov) Officials are also telling people to get tested quickly if they develop a suspicious rash and to notify partners so they can take steps to limit spread. California said it is doing enhanced surveillance and contact tracing as summer travel and large events approach. (sf.gov, cdph.ca.gov) For San Francisco, the immediate message is practical: the first city case of clade I mpox is here, the patient is recovering, and health departments are trying to get more at-risk residents vaccinated before seasonal travel picks up. (sf.gov, cdph.ca.gov)
