A new and possibly deadlier strain of mpox is spreading rapidly across the globe, leading to a public health emergency being declared by the World Health Organization (WHO).
This strain of mpox, known as Clade 1 has spread to many African countries, as well as outside of the continent's borders to Sweden and possibly Pakistan.
Clade 1, formally clade 1 MPXV, was first seen in the Democratic Republic of Congo, and is now also present in the Republic of the Congo, Central African Republic, Burundi, Rwanda, Uganda, Kenya, Cameroon, and Gabon, according to the UK Health Security Agency. Burundi, Kenya, Rwanda and Uganda had not previously seen mpox cases from any clade.
Angola, South Sudan, Tanzania, and Zambia are considered "countries where there may be a risk of Clade 1 mpox exposure," as they share a border with the DRC.
Sweden confirmed the first case of Clade 1 outside of Africa on Thursday, which had been contracted on a visit to one of the African countries currently seeing an outbreak.
"A person who sought care at Region Stockholm has been diagnosed with mpox caused by the clade 1 variant. It is the first case caused by clade I to be diagnosed outside the African continent," Sweden's public health agency said in a statement.
Pakistan may also have a Clade 1 case, though testing is still being performed to confirm if the case is Clade 1 or 2. No cases of Clade 1 mpox have been recorded in the U.S. to date.
There are two clades of mpox—previously known as monkeypox—named Clade 1 and Clade 2. A 2022 outbreak that saw thousands of cases across the U.S., Europe, Australia and many other countries, was the result of Clade 2 mpox.
Clade 1b, a new variant of the Clade 1 strain, is the virus that is currently spreading across Africa, and is thought to cause more severe disease than previous variants.
The DRC alone has seen 15,600 mpox cases—of all clades—and 537 deaths since the start of 2024, with over 96 percent of all global cases and deaths occurring in the DRC, according to the WHO.
"More than 22,000 suspect cases, with more than 1,200 suspected deaths, have been reported in DRC since January 1, 2023, a substantial increase from the median 3,767 suspect clade I mpox cases reported annually in DRC during 2016–2021," the CDC explained.
Mpox is a viral infection that causes painful skin lesions. Direct contact with skin lesions or body fluids is the primary mode of transmission, which can include kissing, sexual contact, or other forms of close physical contact with someone who has the virus. Men who have sex with men are at particular risk of catching the virus.
"Clade 1 monkeypox virus is known for causing more severe disease in young children, pregnant women, and immunocompromised people," Jonas Albarnaz, a Research Fellow specializing in pox viruses at The Pirbright Institute, said in a statement. "The emergence of the new clade 1b variant changed this picture as cases have been reported outside DRC (Burundi, Kenya, Rwanda). Most of the clade 1b has been in young adults, and sexual networks seem to be driving its spread."
However, the virus can also be spread via non-sexual touching, respiratory droplets, and contaminated surfaces like bedding and clothing.
The WHO declared the Clade 1 outbreak to be a public health emergency of international concern on Wednesday.
"The emergence of a new clade of mpox, its rapid spread in eastern DRC, and the reporting of cases in several neighbouring countries are very worrying," WHO Director-General Tedros Adhanom Ghebreyesus said in a statement. "On top of outbreaks of other mpox clades in DRC and other countries in Africa, it's clear that a coordinated international response is needed to stop these outbreaks and save lives."
The U.S. Department of Health and Human Services has said that the risk to people in the U.S. is low.
"Right now, the CDC estimates that risk to the U.S. is low, but as we have seen multiple times over the past few years, infections and outbreaks that start in other countries can quickly spread to the U.S.," Patrick Gavigan, assistant professor of pediatrics and infectious diseases at the Penn State College of Medicine, previously told Newsweek. "It is unclear right now if the current strain/outbreak will spread to the U.S., but people and health care providers should remain cautious and aware of changes in risk level."
There have been a small number of cases of Clade 2 mpox across the U.S., with the virus being detected in wastewater at a handful of locations.
According to the U.S. Department of Health and Human Services, the U.S. has provided "$17 million USD to support clade 1 mpox preparedness and response efforts in Central and Eastern Africa," and plans to donate 50,000 doses of mpox vaccine to the DRC.
"Two main challenges remain: [Firstly,] little is known about the natural history and transmission dynamics of the new clade 1b variant, and this information is key to inform the control strategies," Albarnaz said. "[Secondly,] vaccines exist but their availability is very limited; this represents a major bottleneck for the control strategies."
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