Why the mpox outbreak in the Democratic Republic of Congo is worrying disease docs

"It's just a matter of time, if nothing is done, that the transmission crosses the border in the African region and, again, globally," says Dr. Jean Nachega, an epidemiologist at the University of Pittsburgh.

Nachega is one of a number of public health experts expressing alarm over a major outbreak of mpox – formerly called monkeypox – in the Democratic Republic of Congo.

They say the current situation represents a triple threat.

First, the DRC is seeing record numbers. About 400 suspect cases are reported each week – the majority in children. Second, the strain of the virus that's circulating is especially deadly, with up to 1 in every 10 people who get the virus dying. And third, the virus is behaving differently. Scientists say it is not only surfacing in new areas and new populations (including sex workers), but it's also spreading in new ways – including sexually – and evading diagnostic tests.

Together these issues have made it more urgent – and also more complicated – for the global health community to respond, say mpox specialists.

"For measles, we know what to do. For cholera, we know what to do. For polio, we know what to do. These are things that have been around for a long time. For mpox, a lot of the elements are new," says Dr. Rosamund Lewis, the World Health Organization's technical lead and emergency manager for mpox. "And we don't yet have all the countermeasures in place that we need in place."

A dramatic spike in cases

Last year, the DRC recorded more than 14,500 suspected cases of mpox, and more than 650 deaths. Those figures dwarf previous years – and the numbers continue to rise. In the first two months of this year, there have been more than 3,500 suspected mpox cases and more than 250 deaths.

At this point, the majority of the cases follow a pattern that has become well-established over the past few decades: The outbreaks happen in remote villages in densely forested areas of the north and central DRC. They typically start when the virus jumps from an animal to a person. Imagine a child catching a rodent or a parent cooking bushmeat. And from there, the virus can spread within a household or a community, often through skin-to-skin contact or through contact with shared surfaces, like a bed sheet or towel.

For some, the mpox virus is mild – causing a few lesions. For others, it can be devastating: fever, malaise and painful lesions all over the hands, face and torso – and even death.

"People are very ill, and there's certainly a risk of dying from it or having long-term consequences," says Dr. Anne Rimoin, a professor of epidemiology at UCLA's Fielding School of Public Health who has spent 22 years working on mpox in the DRC.

The strain of the virus that's common in the DRC is called Clade I and it's 10 times more deadly than Clade II, which is found in West Africa and caused the global outbreak. (The nomenclature "Clade" is a scientific way to indicate the strains have a common ancestor.) And with Clade I, about two-thirds of the cases in the DRC are in children under the age of 15.

Lewis, of the WHO, says this could be because many adults have been exposed and acquired some immunity. Plus, anyone who received the smallpox vaccine has some immunity. That vaccine was administered before the disease was eradicated in 1980.

"We've heard about outbreaks in schools. It behaves very much the way other childhood viruses behave," Lewis says. "But we see that high, high death rates are in children. And that is very concerning." So far in 2024, 87% of mpox deaths have been among children under 15 years old.

Experts say it's unclear exactly why there's been such an increase in cases. "I think it's too early to say what exactly is happening here," Rimoin says.

With the number of cases and the number of children impacted, many experts worry about regional spread. Earlier this month, more than 40 mpox infections were reported on the other side of the Congo River in the Republic of Congo. But, so far, Lewis says, it's unclear if those cases came from the DRC, since mpox is endemic in both countries.

A tougher version of mpox

In addition to focusing on children, experts are closely tracking a new situation that doesn't fit the traditional mpox story. Attention has been focused on the gold-rich city of Kamituga in the South Kivu province, which never used to have mpox cases.

"It's a rich region where there are several minerals and thousands of workers working in this mining setting," explains Nachega of the University of Pittsburgh. "We have some recent evidence showing that some miners are circulating this virus and it's been documented also in sex workers."

This is concerning for two reasons, he says. First, the more virulent strain of the virus that's present in the DRC – Clade I – was never known to transmit sexually until a few months ago. Now, this type of spread is firmly established. Second, many of the miners are transient, and many families in the area are on the move too, fleeing violence from ongoing strife.

"This population is highly mobile," says Nachega, noting that when people move viruses move with them and Kamituga is not far from Rwanda, Burundi, Uganda and Tanzania. "We are calling for urgent reinforcement."

He would like to see the DRC and the international community act quickly, improving everything from surveillance to case management. Fast action is especially important when it comes to testing and vaccination, he says.

Tests that might not work

About 90% of the mpox cases in the DRC are not confirmed by a laboratory test. That's because in a country of over 100 million, there are only two labs that do mpox PCR – or polymerase chain reaction – testing.

"You need to collect specimens from the skin and they have to transit [the sample] hundreds of kilometers across very rough roads or down rivers to arrive at the national lab," explains the WHO's Lewis. "There are, as of yet, no fully validated rapid tests. Lots of research is being done on molecular tests, on protein-based tests, but they're not yet at a stage where they can be widely deployed."

She says the result is that most diagnoses are based solely on symptoms, which is problematic. In the forested part of the country, mild mpox can look like chickenpox or measles. In the mining community where it's sexually transmitted, the virus needs to be distinguished from herpes, syphilis and other sexually transmitted diseases.

On top of all that, the specific strain circulating in the mining community has evolved, as viruses do. The part of the genome which the PCR test targets is not present in the current strain.

"So, it's possible to miss the diagnosis," says Lewis. However, she adds that the national lab can adjust to this new reality with testing that reveals the broad type of virus – an orthopoxvirus – and then genome sequencing. The WHO is working to get the word out to neighboring countries.

Vaccine hurdles

Vaccines were a major piece of the strategy during the global mpox outbreak in 2022. However, the DRC government has not authorized use of any of the three vaccines available for mpox – nor has any other African government.

"The need is great," said Lewis. "Everybody wants it to happen very quickly but, at the same time, it has to be done carefully and with quality discussions and quality information." She said she expects it to be several more months, at a minimum, before vaccines arrive in the country.

When the global outbreak happened two years ago, vaccines used for mpox were still relatively new. It was only within the last 10 years – and, in some cases, the last couple years – that places like North America, Japan and Europe approved them. One vaccine used in the U.S. is roughly 82% effective with two doses.

But the data about effectiveness comes from healthy adults in high-income settings. Earlier this month, the WHO's advisory group on immunizations grappled with how this data would apply to children and to adults who may be malnourished or face a different health profile than the one seen in high-income countries. The group ultimately recommended an off-label use in children, given the large number of kids affected by mpox in the DRC.

"The group has been struggling to issue a policy recommendation because there is such a lack of data," says Joachim Hombach, executive secretary of the advisory group.

Several nations have offered to donate doses, and one vaccine manufacturer has drawn up plans to scale up production.

However, experts say, even if an mpox vaccine is licensed, a target population is decided on and supply issues are ironed out, it would still not be easy for the DRC.

"Congo is going through, I think at this point, it must be going through eight or ten different epidemics," says Dr. Michael Ryan, executive director of the WHO's Health Emergency Programme, noting that the country is dealing with measles, cholera, plague and anthrax, among other diseases. "We also have a deep amount of instability in the east of Congo – the peacekeeping operation has shut down there and there are many, many armed groups operating. So ... a very difficult area in which to run any form of health operation, particularly any form of vaccination."

But, he says, the stakes are too high not to take up the challenge of controlling the current mpox outbreak in the DRC.

"This bug is badder and it's more virulent," says Ryan. "We really do need to keep a very, very close eye on it."