How worried should I be about mpox?

The rapid spread of MPOX (formerly known as monkeypox) in Africa has been declared a global emergency.

While new forms of the virus are at the center of concern, big questions remain unanswered.

Is it highly contagious? We don't know. What is the fatality rate? We don't have the data. Will it become a pandemic?

“We need to avoid falling into the trap of thinking there will be another Covid outbreak and we will have another lockdown, or that it will play out like MPOX in 2022,” said Dr Jake Dunning, an MPOX scientist and physician who has treated MPOX patients in the UK.

Despite the uncertainty, to assess the threat we must first recognize that this is not one MPOX outbreak, but three.

These are all happening at the same time, but they affect different groups of people in different ways and cause them to act differently.

These are classified according to “phylogenetic groups,” or essentially which branch of the MPOX virus phylogenetic tree they come from.

• Lineage 1a causes most of the infections in the western and northern parts of the Democratic Republic of Congo (DRC). It is an epidemic that has been ongoing for more than a decade. It is primarily transmitted by eating infected wild animals, known as bushmeat. Infected people can transmit the virus to those with whom they have close contact, particularly children.
• Lineage 1b is a new lineage of the MPOX family that is causing outbreaks in eastern Democratic Republic of the Congo and neighbouring countries. This lineage is spreading along truck transport routes through heterosexual intercourse between exploited sex workers and drivers, who also transmit the virus to their children through close contact.
• Clade 2 was the MPOX outbreak that spread worldwide in 2022, again with a strong association with sex, this time primarily affecting gay, bisexual, and other male communities who have sex with men (In the UK, 98.6% were men.We are also urging those who have been in close contact with the infected person to be vigilant. This outbreak is not over yet.

The World Health Organization has listed lineage 1b as one of the main reasons for declaring it a Public Health Emergency of International Concern, as it has spread to countries not previously affected by MPOX, including Burundi, Kenya, Rwanda and Uganda.

It was first reported this year, but genetic analysis has traced its origins back to September 2023 in Kamituga, a gold mining town in South Kivu province in the Democratic Republic of Congo.

“There is a sex industry in the mining towns, which is spreading rapidly to border countries due to mass movements of people,” Leandré Murfula Masirika, a research coordinator at the health department, told me in South Kivu.

He said the virus was mainly spread through paid sex, but then passed from parent to child and between children, and was also linked to miscarriages.

The occurrence of this new lineage 1b offshoot appears to be significantly different from lineage 1a.

“This one is really different because the rash is more severe and the disease seems to last longer, but above all this is caused by sexual transmission and person-to-person contact and there has been no confirmed link to bushmeat whatsoever,” Professor Trudy Lang, from the University of Oxford, told me on Radio 4's Inside Health programme.

The key question is “why?” The answer is either evolution or opportunity.

The new strain appears to be genetically different, but so far there is no convincing evidence that these mutations make the virus itself more transmissible.

If sex workers, who have close contact with many people, become infected, this will accelerate the spread of the virus.

“Sexual transmission may occur more rapidly, but that does not necessarily mean that the virus itself is more infectious.” Dr Rosamund Lewis saysMPOX Leader at the World Health Organization.

The virus is not a typical sexually transmitted disease, but it is transmitted by close physical contact, and sex naturally involves close contact.

There is also uncertainty about how deadly the current outbreak is.

Not all deaths are recorded because some people seek “traditional” medical treatment rather than hospital care, and it is not known how many people are infected, some of whom may have only mild symptoms or may be asymptomatic.

“We don't know how many cases there are, and to me that's one of the biggest unknowns,” Prof Lang said.

History suggests that lineage 1 outbreaks are more dangerous than lineage 2 outbreaks. In previous outbreaks, up to 10% of people with lineage 1 mpox died, although it is unclear how relevant that 10% figure is to the current outbreak.

Mortality isn't just caused by the virus: malnutrition, untreated HIV which damages the immune system, and lack of access to hospital care all contribute to deaths.

The World Health Organization says In 2024, lineage 1a caused deaths in 3.6% of known MPOX cases, with no comparable figures for the new lineage 1b.

The MPOX outbreak in the Democratic Republic of Congo this year has already killed more than 500 people, and the threat to the country and its neighbours is clear.

“The virus is not under control in South Kivu,” says Leandre Murfula Masirika.

“Massive intervention is needed to control and stop this epidemic.”

Professor Lang, who is working with a team in the Democratic Republic of Congo, draws a comparison to the early days of HIV, and when I challenge this, he says it's “a word that's not used very often, and it's not a word that's used lightly”.

She says: “The young sex workers who are being exploited, their families, the truck drivers and, of course, the children around them who are the first victims of this outbreak. This is exactly the same situation as in the early days of HIV, where the infection was perpetuated by trucking routes.”

Mpox is not expected to become a COVID-level event, and it has already been nearly a year since new variants emerged in September 2023.

The most likely scenario in the UK and similar countries is that someone returns home with the virus and falls ill.

Similar incidents have happened many times in the past with mpox in the UK, Cases of mpox continue to be reported It is linked to the emergence of clade 2 in 2022.

These imported cases may be the end of the epidemic, or there may be limited household spread through close physical contact. Sweden was the first country outside of Africa to report cases of lineage 1b, but no further spread has been reported.

An even bigger concern is that infected young children could bring the virus to daycare or kindergarten where they play with other children and spread the infection there.

This is the limit of what is considered possible in the UK.

“No, I don't think this is going to be a big thing,” Dr. Jake Dunning said.

“I find it a little frustrating and disturbing that some people are only looking at what happened in 2022 and thinking the same thing is going to happen again.”

A possible response would be to identify and vaccinate people who have come into contact with infected people, rather than through a mass vaccination program.

Managing imported cases like this should be easier in the UK than in the Democratic Republic of Congo, which has the added challenges of conflict and humanitarian challenges.

There is no specific vaccine for smallpox yet, but the smallpox vaccine is effective against smallpox.

Both smallpox and monkeypox viruses are orthopoxviruses, and immunity to one confers protection from the other.

The end of smallpox vaccination campaigns after smallpox was eradicated in 1979 is one of the reasons for the current surge in smallpox cases.

People who received the smallpox vaccine as children should still have some protection, even though their immune systems are aging.

The same is true for men who received the vaccine during the 2022 outbreak, but the lineage 1 outbreak has not disproportionately affected gay, bisexual, or men who have sex with men.

The people who need the vaccine most are at the epicenter of the outbreak in Africa.

Dr Dunning said: “We have been absolutely terrible about sharing the tools we have to prevent MPOX, particularly the vaccine, and there is no excuse for that.”

“Clearly our biggest win will be getting control of these infections at their source.”