Scientists briefing journalists about the current outbreak said they feared the new vstrain was being spread more easily, causing more serious disease and more deaths in children and adults.
There is also concern over the risk of asymptomatic spread between people who do not have symptoms and are unaware they have the virus.
The current case figures are “the tip of the iceberg”, said Prof Trudie Lang, professor of global health research at the University of Oxford.
“It’s definitely the most dangerous strain yet.
“We don’t know how many non-severe cases are hidden.”
It is also not clear how fast the new strain spreads or whether current vaccines will protect against it. Trials will be needed to work this out, which will take time.
The global outbreak of mpox that spread across Europe and America in 2022 was sexually transmitted and driven by men who have sex with men. It was caused by the Clade II mpox virus.
The new strain is from the more deadly Clade I but is distinct from other outbreaks which have previously affected the region. It can also be spread through non-sexual contact, which makes it more dangerous.
Many children have been infected, including newborn babies during pregnancy.
There have been reports of a small number of infected pregnant women miscarrying their babies.
And some patients have been left with long-term complications with their eyes, skin and genitals.
One healthcare worker looking after an infected patient is reported to have lost her sight after becoming infected herself.
In cases in DR Congo to date, the new strain has a mortality rate of 4% in adults and 10% in children.
