Rare Mpox Strain Detected In San Francisco
- Health officials reported a spike in mpox cases, with a rare strain identified in San Francisco. - The newly detected strain is the first confirmed case in San Francisco, prompting vaccination advice. - Officials urged Californians to get vaccinated and monitor symptoms amid rising cases statewide. (patch.com)
Mpox is a virus that usually spreads through close skin-to-skin contact, and San Francisco has now confirmed its first case of clade I, a rarer strain. (sf.gov) San Francisco health officials said April 16 that the case was confirmed on April 14 in an unvaccinated adult resident. The patient was hospitalized, is improving, and 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 California since November 2024 and the first in San Francisco. They said public health teams are doing enhanced surveillance and contact tracing. (cdph.ca.gov) The strain matters because the 2022 outbreak in the United States was driven by clade II, not clade I. San Francisco said both types can cause fever, swollen lymph nodes, fatigue, and a rash that looks like pimples or blisters. (sf.gov) California said clade II is still the strain circulating more broadly, and the state is averaging 14.5 weekly clade II cases so far in 2026, up from 5.8 in 2024 and 3.4 in 2025. The state said most of those infections have occurred in people who were unvaccinated. (cdph.ca.gov) Health officials are urging people at higher risk to get both doses of the Jynneos vaccine, which San Francisco and California said protects against both clade I and clade II. San Francisco said the vaccine is available through health care providers, local pharmacies, and city-listed sites for people who have trouble accessing care. (sf.gov) The Centers for Disease Control and Prevention tracks both clade I and clade II in its national case data, and California’s mpox dashboard says state case data are refreshed every other week. KQED reported April 17 that the San Francisco case was the 16th clade I case identified in the United States so far. (cdc.gov) (cdph.ca.gov) (kqed.org) San Francisco health officials said exposure risk remains low for people who are not in higher-risk groups, but they tied the vaccination push to summer travel and events. People with a new rash that looks like mpox are being told to contact a health care provider and alert partners so they can take steps to limit spread. (sf.gov)
