Officials from California have confirmed that a resident of Long Beach has tested positive for “clade I mpox,” marking a significant shift in the understanding of the virus’s transmission. In a related development, Los Angeles health officials announced a second case fitting the same profile, as reported by the Associated Press.

Both individuals from California, whose identities have not been disclosed, required hospital care but are currently in isolation and recovering at home. Jennifer Ann Gonzalez, acting public affairs officer for the Long Beach health department, noted that there has not yet been any established connection between the two cases.

While Long Beach is geographically part of Los Angeles County, it operates its own city health department. Investigators in Long Beach have so far been unable to identify any close contacts of the patient who have traveled abroad, and no additional cases have been confirmed. In response, a few of the patient’s close contacts have received vaccinations, according to Nora Balanji, the communicable disease coordinator for the Long Beach department.

Long Beach is located in Los Angeles County but has its own city health department. Investigators there say they have not found a close contact who traveled abroad, nor have they confirmed additional cases. A few of the person’s close contacts have been given a vaccine, said Nora Balanji, the Long Beach department’s communicable disease coordinator.

It’s not the first U.S. case of clade I mpox. Six cases of the disease have been documented in the U.S. before this week, but all six were from international travelers who officials believe were infected while abroad. The disease first made its way to the U.S. in 2024, according to the Centers for Disease Control and Prevention.

Clade I mpox is considered more severe and dangerous than the more common clade II variant, according to the Los Angeles County Public Health Department. 

Milder symptoms can include fever, chills and body aches. In more serious cases, people can develop lesions on the face, hands, chest and genitals.

The clade I variant is also significantly more deadly than its more common counterpart. Johns Hopkins University notes that the mortality rate for clade I mpox is somewhere between 1% and 10%, while the mortality rate for clade II infections has ranged from less than 1% to 4%.

But public health officials say the risk to the public is low, and that the disease can be combatted effectively with a vaccine. 

Mpox — which was renamed from monkeypox in 2022 over racism concerns — is a rare disease caused by infection with a virus that is in the same family as the one that causes smallpox. It is endemic in parts of Africa.

One version of the virus — called clade II — was the source of an international health crisis in 2022, when infections escalated in dozens of countries, mostly among men who have sex with men. At one point, the U.S. was averaging close to 500 cases per day.

The infections were rarely fatal, but many people suffered painful skin lesions for weeks. Those outbreaks waned later that year, thanks in part to the Jynneos vaccine made by Bavarian Nordic.

The other version — known as clade I — likewise can spread through sex, but also through other forms of contact. In Africa it has infected a broader range of people, including children.

A newer form of the clade I virus has been widely transmitted in eastern and central Africa. The World Health Organization declared the situation a public health emergency, but last month it said the problem had waned enough that it was no longer an international emergency.

Still, “it’s concerning if this virus has come here and now is starting to be transmitted from person to person,” said Dr. William Schaffner, an infectious diseases expert at Vanderbilt University.

The Associated Press contributed to this story.