First Mpox Clade I Case Confirmed in California

The California Department of Public Health (CDPH) today announced it had identified the first known case of clade I mpox in the United States. This case was confirmed in an individual who recently traveled from Africa and is related to the ongoing outbreak of clade I mpox in Central and Eastern Africa. Historically, clade I has caused more severe illness than clade II.

The clade II outbreak began worldwide in May 2022, reaching Boston in late May.

As of November 9, 2024, 2,410 clade II cases have been confirmed in the U.S. this year. This is a significant increase compared with last year, when 1,267 mpox cases were reported.

The CDPH stated on November 16, 2024, the affected individual received health care in San Mateo County. The individual is isolating at home and recovering. Public health workers are contacting people who had close contact with this individual.

According to the U.S. CDC, there is no concern or evidence that mpox clade I is spreading between individuals in California or other states. 

Bavarian Nordic's JYNNEOS® (MVA-BN®) mpox/smallpox vaccine has been effective against clade II and is commercially available at clinics and pharmacies in the U.S.