US public health officials are on alert due to the detection of a newer variant of mpox, known as clade Ib, which is beginning to spread within communities in the US and Europe. While the immediate risk to the general public is considered low, the emergence of community transmission in new locations presents challenges for public health in identifying and containing the virus.
In October, three cases of this newer variant were reported in California, with two individuals in Los Angeles and one in Long Beach requiring hospitalization but now recovering. Crucially, these patients had no apparent links to each other and had not traveled internationally, indicating that the virus is likely circulating undetected within some communities. This marks the first instance of community spread of the new variant in the US, following earlier detections among travelers.
Several European countries, including Spain, Italy, the Netherlands, and Portugal, have also reported apparent community transmission of the newer mpox variant, while the older variant continues its global circulation. The World Health Organization has recorded over 44,000 mpox cases globally in 2025, exceeding the total for 2024. The California cases may be genomically linked and potentially trace back to an August travel case, according to an advisory from the US Centers for Disease Control and Prevention (CDC).
Experts suggest that the hospitalization of the California patients lends credence to the idea of local transmission. They also note that the effectiveness of vaccination in preventing infection and causing less severe disease could make passive surveillance more difficult, as individuals with milder symptoms might be less likely to seek treatment or even suspect they have mpox. This necessitates a more proactive approach to case detection and monitoring.
The new variant, which emerged around mid-2023 and was first identified in the Democratic Republic of the Congo, differs from the clade IIb variant that caused a major outbreak in 2022. While the 2022 outbreak was predominantly among men who have sex with men, the new variant has infected men and women at similar rates, typically between the ages of 25 and 40. It appears to spread through "dense sexual networks" or individuals with multiple sexual partners, although it is difficult to predict if this pattern will hold true in other regions.
While California has not released specific demographic information for the current cases, an earlier press release indicated the newer variant was primarily affecting communities of gay and bisexual men, as well as their social networks. The CDC identifies individuals at higher risk as those who are gay, bisexual, men who have sex with men, transgender or nonbinary, and have had multiple partners in the past six months, or who have visited sex venues or attended large events where mpox is spreading. Mpox spreads through close skin-to-skin contact, making sexual contact a primary mode of transmission.
Public health officials are emphasizing vaccination as a key preventative measure for at-risk populations. The accessibility of vaccines, particularly in low-resource communities, is enhanced when provided by the government and offered outside of traditional working hours and in easily accessible locations. The current political climate, includi... download the app to read more
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