This outbreak came as a total surprise: most cases were reported from non-endemic countries, mostly in men who have sex with men who had become infected during recent sexual encounters.
Even though most cases were clinically not particularly severe and the death toll stands at just over 200, the global outbreak was declared a public health emergency of international concern by the World Health Organization on 23 July 2022.
Fortunately, case numbers soon plummeted due to a combination of behavioural changes and vaccination in at-risk groups.
Modern vaccines and antiviral drugs with activity against mpox were made available in many affected high-income countries.
These had been developed and stockpiled in the US and Europe, mostly in preparation for a potential bioweapon attack using a poxvirus.
The global outbreak in 2022 was caused by clade II of MPXV, which is endemic in west Africa and not as virulent as clade I MPXV, which so far has only been seen in the Congo Basin.
That first mpox public health emergency of international concern was declared over in May 2023.
Clade II MPXV infections are still occurring globally, but the worst seems over – for now.
Complacency would be misguided, as illustrated by the current mpox outbreak that is gathering steam.
Upsurge in Africa
The African region is experiencing an upsurge in mpox cases which started in 2023.
As the continent which includes the areas where mpox has been endemic for a long time, Africa now presents a complex mosaic:
cases arising from the endemic, largely zoonotic, pattern that used to be predominant in the past
cases linked to the 2022 global outbreak, for example in South Africa
most worryingly, ever increasing numbers of MPXV clade Ib infections reported from the Democratic Republic of Congo.
New, more dangerous strain
The current clade I MPXV (formerly called Congo Basin strain) is more virulent than the clade II (west African) strain, resulting in a higher case fatality rate.
The ongoing outbreak has its epicentre in South Kivu province, eastern DRC, and has the potential to fuel a large pandemic.
*It has a distinct epidemiological pattern with sustained chains of human-to-human transmission, often via the sexual route.
*It may have increased transmissibility (we don’t know yet).
*The virus which causes it is the newly defined clade Ib lineage. It displays mutations that are the hallmark of human-to-human spread that is estimated to have been happening since September 2023.
*Case numbers are rising rapidly, even though many suspected cases are likely not tested and thus not counted as confirmed. Complicating matters, a commonly used test was found to miss infections with this lineage of the virus.
*It affects mostly adults.
*The case fatality rate is higher than it was in the 2022 global outbreak.