Mpox is what’s called a zoonotic virus: a disease in humans that was initially transmitted from animals. It was previously known as monkeypox, a name that has been retired both because it is misleading – it is most often found in rodents – and because the racist connotations of the term were stigmatising and confusing.
Mpox is mostly spread via prolonged skin-to-skin contact, and causes flu-like symptoms and skin lesions. Most infections pass on their own and are mild – but severe cases can cause sepsis and blood poisoning and can be fatal, with the greatest risk to those whose immune systems are already weakened.
The current outbreak is centred on DRC, where 96% of all cases and deaths have been found, but it has now spread to 13 African countries. “This is far and away the biggest outbreak of mpox ever, with quite a high fatality rate,” Michael Marks said. “It’s not likely to lead to a Covid-19 style pandemic. There will be concerns about its spread in countries with more resources, but it’s chiefly going to be a problem in the region.”
How is this outbreak different from the one in 2022?
There have been occasional outbreaks of mpox in DRC, Nigeria and other African countries for decades. Two years ago, cases quickly started being recorded around the world, with more than 95,000, leading to more than 150 deaths in 115 non-endemic countries. Men who have sex with men were most at risk. (Although mpox is not technically an STD, sex tended to be a vector because of the likelihood of prolonged skin contact.)
There are two main “clades”, or variants, of mpox. Clade II, which caused the 2022 outbreak, “historically circulates in west Africa and has a much lower mortality rate – below 1%,” Marks said. “Whereas the virus in central Africa, clade I, has a higher mortality rate – between 1 and 10% in different studies. The most recent data from DRC shows the mortality rate at about 4%. That’s substantially higher than the 2022 outbreak.”
Another important feature of the new outbreak is the emergence of a new subvariant, clade Ib. It has about the same 4% mortality rate, but appears to be passed on more rapidly.
“It is possible that there is some intrinsic change in the virus that makes this particular strain more likely to spread human-to-human,” Marks said. “But it’s also possible that this strain has got into transmission networks that are particularly well-suited to sustaining transmission. The exact balance between those things is unclear.
“A reasonable proportion of the initial spread in DRC appears to be between female sex workers and their clients, and people having multiple partners may spread it quickly. And then you have lots of internally displaced people in crowded conditions, which is again a dynamic that favours much faster transmission.”
Which parts of the world are most severely affected?
At the moment, DRC is by far the worst affected country, with its neighbours also facing the possibility of significant outbreaks. While the case in Sweden is cause for concern and there will probably be some spread to other countries in the developed world, the impact is likely to be much less, Marks said. “In most circumstances, the risk of importation to countries like Sweden leading to prolonged chains of transmission is quite low.”
In Europe or North America, there are not large-scale camps for internally displaced people with a high risk of transmission. And gay and bisexual men who were vaccinated during the 2022 outbreak should still have some protection if the disease does enter those networks, further blunting its spread.
“If nothing changes, the likelihood is that there will be many more cases in DRC, and many more deaths, with sustained importation of the virus because of a huge amount of movement across porous borders to neighbouring countries,” said Marks. “And there will be a small number of cases exported to higher income countries, which occasionally lead to onward transmission.”
What can be done to counter its spread?
The World Health Organization’s declaration of a global public health emergency, after a similar declaration for Africa by the Africa Centers for Disease Control and Prevention (Africa CDC), is important, Marks said: “It unlocks a number of things. It brings attention, it brings emergency funding mechanisms, better government coordination, and easier vaccine procurement. And it’s through vaccination above all that the dynamic of the epidemic could be substantially changed.”
You will remember the R number from the coronavirus pandemic: an R of one means that each infected person passes the disease on to one other, on average. An R below one means the virus will peter out; the higher it is above one, the faster the spread. Because mpox is not a respiratory virus, and because there does not appear to be much transmission by people who have the infection but not yet symptoms, the R number is not much above one. That’s why it is unlikely to become a global pandemic.
“It’s not like Covid or flu where the natural number is four or five and it takes a huge effort to get it down,” Marks said. “Good public health interventions should be able to significantly alter the spread. The difficulty is that some of the people with mild symptoms won’t assume that it’s mpox.”
Effective public health messaging can also help, giving people the information they need to avoid contracting the virus if possible. So will tools like contact tracing, which aim to find those who have been in contact with known carriers so they can isolate and interrupt the chain of transmission. “But while that’s likely to help somewhere like the UK, it is much less useful with children living in a camp for internally displaced people in DRC.”
Are we prepared?
It depends who you mean by “we”. The US and European countries have stockpiles of vaccines, and Bavarian Nordic, the manufacturer of one of two WHO approved jabs, says it has enough production capacity to meet demand.
But while Africa CDC has been given $10.4m by the Africa Union to fund its response and says it has a plan to secure 3m doses of vaccine this year, Reuters reported that only 65,000 doses are likely to be available in the short term in DRC, with a full rollout unlikely to begin before October.
“There hasn’t been a release of adequate funding or vaccination to control this in the most affected countries,” Marks said. “The teams in DRC are very experienced, and with the right resources, they can handle it. But what’s required is vaccine access. If you contrast the situation to the rapidity with which we were able to roll out vaccination in the UK within a few months of the last outbreak starting, the supply of vaccine in DRC is clearly woeful.”
Marks described a fundamental problem with attitudes in the developed world to funding such vaccine rollouts: in 2022, a WHO appeal for $34m to fight mpox got no take-up from donors.
“They respond through a global health security perspective, by only acting to stop something coming here instead of because health is a basic human right,” Marks said. “But actually, that approach means that you let things get very bad before you act, and then it takes a much larger effort and is much more costly to control. That is about the politics, not the science, and it’s very difficult to persuade people to make those kinds of long-term investments.”
