NBC News
The World Health Organization’s decision to declare mpox—also known as monkeypox—a global public health emergency for the second time in two years may seem like a déjà vu. But there are important differences between the strain causing concern now and the one that spread in 2022.
MPox is a viral infection characterized by painful skin lesions. It is transmitted by direct contact with an infected person, an animal, or contaminated items such as clothing or bedding.
The virus is classified into two distinct groups: clade I and clade 2. The latter variant was responsible for the 2022 outbreak, when nearly 100,000 cases were recorded worldwide.
The current alert is for a clade I variant. The outbreak began in January 2023 in the Democratic Republic of the Congo and has since spread to 12 other countries in the region.
Sweden confirmed the first known clade I infection outside Africa on Thursday. Health officials said the person became infected after a trip to the continent. Pakistani health officials also confirmed a case on Friday but have not yet identified the strain.
Clade I is more contagious than clade 2 and may be more severe, so infectious disease experts are concerned about further international spread.
“We should have learned one lesson from 2022: An infection anywhere is potentially an infection everywhere,” said Anne Rimoin, a professor of epidemiology at the Fielding School of Public Health at the University of California, Los Angeles.
How does this mpox variant spread?
MPOX has been spread in several ways. First, through direct contact with an infected person, either skin to skin, saliva, or mucus. Second, through contact with contaminated objects. And third, through contact with infected animals: hunting, trapping, or cooking them, touching sick rodents, or receiving bites or scratches.
In 2022, the version of clade 2 that spread worldwide, called clade 2b, was transmitted primarily through sexual contact.
Recently, in the Democratic Republic of Congo, clade Ib has also spread through sexual contact between sex workers and men who have sex with men. Research that has not yet been published or peer-reviewed linked an outbreak in a mining town in eastern Congo to sex work in bars.
But that’s not the only way the virus is transmitted. Dr. Stuart Isaacs, a professor of medicine at the University of Pennsylvania, said much of the spread of clade I could be due to contact with animals and transmission within households. But it’s hard to know for sure because of poor surveillance in the regions where the outbreak has been identified.
What is known from current evidence is that clade Ib spreads more easily, Isaacs added.
How serious are the recent cases?
In the past, clade I outbreaks have been more lethal than clade 2 outbreaks, killing up to 10% of people who became ill. But more recent outbreaks have had even lower mortality rates: Of an estimated 22,000 cases in the Congo, more than 1,200 people have died, putting the mortality rate at just over 5%.
In contrast, clade 2 outbreaks in Africa have typically had a case fatality rate of around 1%, and only 0.2% of cases linked to the 2022 global outbreak were fatal.
Rimoin said the severity of the disease “may have less to do with the clade itself and more to do with the route of transmission, the immune system of the individual, and the source of the infection.”
The health threat in the United States may be milder than in Africa, according to Marc Siegel, an associate professor at the George Washington School of Medicine and Health Sciences.
“The underlying health conditions of the population in the DRC are likely contributing to the current case fatality rate,” he said. “With less malnutrition and better access to healthcare resources, I imagine the case fatality rate will not be as high as what we are seeing in the DRC,” he added.
Monkeypox vaccines are also much more widely available in the United States following a major distribution effort in 2022. Two doses of the mpox vaccine — or prior clade 2 infection — should be enough to protect people against severe disease caused by clade I, the Department of Health reported Wednesday.
Do mpox symptoms differ between variants?
Symptoms of clade I and 2 can be difficult to distinguish.
The disease typically begins with a rash that progresses to small bumps on the skin, followed by blisters that fill with a whitish fluid (a hallmark of the disease) and eventually form crusts. People may also experience fever, headache, muscle aches, back pain, lack of energy, and swollen lymph nodes.
These symptoms usually go away on their own within a few weeks. But in severe cases, people may develop larger and more widespread lesions, secondary bacterial infections, pneumonia, heart inflammation, or brain swelling. Immunocompromised people may develop atypical symptoms and are at higher risk for hospitalization and death.
Historically, mpox lesions tended to appear on the face, chest, palms, and soles of the feet. However, during the 2022 outbreak, people frequently developed lesions around the genital and anal region or inside the mouth and throat, presumably due to the way the virus was spreading at the time. Lesions were also fewer in number and less pronounced overall.
Some such cases have also been detected in the current outbreak in the Congo.
“There are reportedly more people with genital lesions this time than in previous clade I outbreaks,” said Amira Albert Roess, a professor of global health and epidemiology at George Mason University. “It will take us some time to really understand what may be happening.”
