A potentially more dangerous strain of the mpox virus has emerged in Northern California, prompting health officials to urge vaccinations, particularly for those at higher risk. The clade I strain was confirmed for the first time in San Francisco on April 14, with an unvaccinated adult who had close contact with someone who had recently traveled internationally requiring hospitalization.
The Threat
Clade I is considered potentially more dangerous than the more common clade II strain. It causes more serious illnesses and is linked to more deaths, according to the World Health Organization. It is the seventh clade I mpox case in California, with previous cases reported in Los Angeles and San Mateo counties. Since 2022, clade II mpox has been circulating at low levels in California, with the state reporting 7,349 cases from both strains. About 350 people have required hospitalization.
Symptoms and Spread
People usually get sick within 21 days of exposure to the mpox virus. Most people with mpox experience flu-like symptoms for a few days before developing a rash on their hands, feet, chest, face, mouth or near the genitals. The rash can look like pimples or blisters at first and may be painful or itchy. Mpox mainly spreads through sex or close contact with a person with mpox infection, though direct contact with rashes, scabs, or body fluids can also spread the virus.
Prevention and Treatment
The mpox vaccine is the best protection against both strains and significantly reduces the chance of infection while helping prevent severe illness, hospitalization, and death. The vaccine requires two doses and can potentially be effective even after exposure. Most people recover from mpox with pain management and supportive care. The World Health Organization phased out the name “monkeypox” in 2022 in favor of mpox because of “racist and stigmatizing language” online during an earlier outbreak.
This article is an AI-assisted summary. All facts and figures are drawn from the original report: https://www.bostonherald.com/2026/04/20/dangerous-mpox-clade-california-vaccinations-urged/