San Francisco Detects First Clade I Mpox Case; Health Officials Reassure Low Public Risk

San Francisco reported its first case of Clade I mpox in a resident on April 16, 2026. 

The San Francisco Department of Public Health (SFDPH) confirmed the first case of mpox in an unvaccinated adult. The person was hospitalized, and their health condition is improving, the department said. 

The patient reported close contact with an individual who had traveled internationally, according to the SFDPH. 

No further details about the patient were available.  

What is mpox?

Mpox, formerly known as monkeypox, is caused by the monkeypox virus and belongs to the same family of viruses as the smallpox virus, according to MedlinePlus. 

The viral infection can spread between animals (typically small rodents and monkeys) and people. The infection primarily spreads between people, usually through close contact, and sometimes through objects and surfaces that have been touched by a person with mpox, according to the World Health Organization. 

In San Francisco, mpox cases have usually risen in the summer and fall months every year since 2022. 

There are two types of mpox viruses: 

• Clade I: Mostly found in Central and Eastern Africa. This type is more severe and has high mortality. Between November 2024 and February 2026, 11 cases of Clade 1 mpox were reported in the U.S., according to the Centers for Disease Control and Prevention (CDC). 

• Clade II: Mostly found in West Africa. Infections caused by this type are usually less severe, with higher chances of survival. This type of mpox caused the outbreak of mpox in 2022, but has decreased over the years. In 2025, there was an uptick in Clade 11 mpox cases across the U.S., according to the CDC. Between 2023 and 2025, around 1,700 to 2,800 Clade II mpox cases were reported in the U.S. annually. 

While Clade I mpox cases in the U.S. are rare, Clade II cases continue to occur in San Francisco and throughout California, according to the SFDPH. 

In the U.S., both types of the virus usually spread through close skin-to-skin contact, including during sexual activity. 

Mpox spreads in the following ways: 

• Close, personal contact with a person who already has the virus. This includes touching, exchanging body fluids, and during intimate physical contact. 

• During pregnancy, from the mother to the fetus. 

• From infected animals, by being scratched or bitten by an infected animal, or by preparing or consuming meat of an infected animal. 

Symptoms include a rash with sores, fever, chills, swollen lymph nodes, muscle aches, and exhaustion. 

Mpox Vaccines

The SFDPH urged people at risk for mpox to receive both doses of the vaccine. Currently, the risk of mpox exposure is low for those who are not in higher-risk groups. 

The vaccine is available at local pharmacies and through healthcare facilities. 

In addition to providing the “best protection” against the mpox virus, the vaccine also protects against both Clade I and Clade II types of the virus. This ensures that a person is protected from all types of the virus, irrespective of which type is circulating, where they live, or where they are traveling. 

WHO recommends MVA-BN or LC16 vaccines for people at risk during an outbreak of mpox.

Comprising two doses, the vaccine can be administered four weeks apart. There is no third dose of the vaccine.