The first U.S. case of a potentially more severe type of mpox (formerly monkeypox), known as Clade I, was reported near San Francisco in November. The patient had recently traveled from eastern Africa, where there is an ongoing Clade I mpox outbreak. The individual, who had mild illness, was treated at a local medical facility and isolated at home while recovering.

 

There are two major strains of mpox, Clade I and Clade II. The latter was responsible for the global outbreak in 2022, which mainly affected gay and bisexual men. This strain continues to circulate at a low level in the United States. Concurrent Clade I mpox outbreaks are underway in the Democratic Republic of the Congo and nearby countries. One (due to Clade Ia) mainly affects children via household transmission and contact with wild animals, while the other (due to Clade Ib) appears to be largely driven by sexual transmission. Clade I mpox has historically had a higher fatality rate than Clade II, but mortality depends on access to medical care.

 

Health officials consider the risk of a Clade I mpox outbreak in the United States to be low, but they’re urging people at higher risk to get vaccinated. These include men who have sex with men, transgender and nonbinary individuals, people living with HIV, those using or eligible for HIV pre-exposure prophylaxis (PrEP), sex workers and others in their sexual networks. Two doses of the Jynneos vaccine should be given at least four weeks apart. Booster doses are not recommended for those who have completed the two-dose series, and people who have already had mpox do not need to be vaccinated. Evidence indicates that the vaccine protects against both Clade I and Clade II mpox.