Editor's Note: This report has been updated to provide further clarity regarding a Congo province referred to by Sylvie Jonckheere.
Global health authorities are sounding the alarm over a variant of mpox spreading in the Democratic Republic of Congo. Little is known about the mutation, other than that it appears to spread more easily among people.
The mpox virus circulating in the North and South Kivu provinces of Congo is believed to have mutated from the lineage – clade I – endemic to Central Africa, and is distinct from the strain – descended from clade II – that struck the US and other Western countries in 2022 and 2023.
According to the World Health Organization (WHO), the risk of mpox in Congo is still high. The recently discovered mpox strain is expected to have emerged around September 2023.
Although more is still being learned, the virus appears to have some worrying characteristics.
“The main difference and what we see or can confirm with epidemiology is that there is persistent human-to-human transmission. It has been going on for months now and that is really new for clade I,” said Sylvie Jonckheere, an emerging infectious diseases advisor for Doctors Without Borders who is currently based in Goma, Congo.
Clade I mpox is transmitted primarily from animals to humans as a zoonotic disease and generally has a higher mortality rate than clade II, with up to 10 percent of infections resulting in death.
The WHO noted that the clade I strain has mutations that indicate “viral adaptation due to circulation among humans.” Unlike COVID-19, the mpox virus is not known to mutate rapidly.
William Schaffner, a spokesman for the National Foundation for Infectious Diseases, said MPOX is more like measles, for which one vaccination is typically enough to last a lifetime, in terms of how easily it mutates.
“Certainly, a large outbreak, a large outbreak of mpox like we're seeing now, has not been recorded before. There have been sporadic cases, of course, but nothing like this,” Schaffner said. “This is a very unique outbreak. It doesn't appear to be a virus that mutates rapidly, but we have seen what I'm sure is a consequence of a mutation.”
Unlike the mpox variant that spread through Western countries in 2022, the newer variant does not appear to be strongly linked to sexual transmission or the social networks of men who have sex with men.
According to Jonckheere, about 25 percent of cases occur in children. But the mpox virus circulating in eastern Congo does not appear to cause more serious illness.
“It's not actually more serious, the mortality rate. So the lethality of this disease is still quite low for now in the eastern part of Congo compared to what we saw in Équateur, historically or even recently,” Jonckheere said, referring to a province in Congo.
Broadcasts such as the BBC have reported that this mpox mutation could be the “most dangerous strain to date.” Jonckheere said it depends on “how you define ‘dangerous,’” and noted that the current lack of comprehensive information on this mutated strain “warrants a grain of salt, maybe even a little more than a grain.”
“It seems more likely to be human-to-human transmission. It will follow people wherever they go,” she said. “In this part of Congo, there's also a lot of movement between countries, so it could spread further. But if you look at deaths or mortality or things like that, it's not more dangerous. So it really depends on how you define it.”
One factor not helping the outbreak is the inability to maintain adequate social distancing.
“There is no option to keep distance in any way. People are living, you know, seven to a four-square-meter shelter, literally,” said Jonckheere, who noted a lack of clean water, as well as sexual or transactional contact, as other factors exacerbating the spread of mpox in the region.
At present, it appears that this mpox variant is confined to Congo, although the region in which the virus is located borders both Burundi and Rwanda, raising the possibility of infections outside the country.
Jonckheere noted that its spread is assessed as a regional threat.
Vaccination efforts are underway in Congo. Schaffner noted that the smallpox vaccine used in the U.S. during the 2022 MPOX outbreak should still be effective against the mutated strain.
Although mpox is no longer considered a public health emergency in the U.S., WHO still considers it a “moderate” threat in countries with historical transmission and their neighbors. The general population in countries that were not affected before the outbreak that began in 2022 is considered low risk.
A WHO report from June noted 646 laboratory-confirmed cases of all types of mpox reported in 26 countries in May, an increase from the previous month.
Because the number of reports of the virus has declined since 2022, the current estimate of the number of cases is believed to be an underestimate.
“It remains a concern. I mean, the epidemic curve has started to rise, has peaked and has come down tremendously, tremendously, tremendously, but it has never gone away,” Schaffner said. “There have been, I think, no reports in neighboring countries. And there have been no reports to date of exports to Europe, Canada, the United States or elsewhere. But public health is obviously following this very closely, because it has that potential.”
Updated July 9 at 10:49 a.m. EDT
