Of the more than 30,000 suspected cases reported in Africa this year, barely 40% had been confirmed through a test, the WHO said.
Yukiko Nakatani, the WHO’s assistant director-general, described the new diagnostic test as “a significant milestone”.
“Increasing access to quality-assured medical products is central to our efforts in assisting countries to contain the spread of the virus and protect their people, especially in underserved regions,” she added.
The breakthrough comes as the Democratic Republic of the Congo, where the highest number of cases has been reported, prepares to begin an mpox vaccination programme on Saturday.
Mpox, which is a highly contagious disease, has killed at least 635 people in that country this year.
In August, the outbreak of the virus was declared a global public health emergency by the WHO for the second time in two years, following rising cases in DR Congo and its spread to neighbouring Burundi, Uganda and Rwanda.
Some Western countries have donated doses of mpox vaccines to combat the outbreak of the disease in Africa but reports say more are urgently needed.
Rwanda, which was the first to administer mpox vaccines in Africa last month, is set to receive 5,000 more doses on Friday, according to the Africa Centres for Disease Control and Prevention (Africa CDC).
In Nigeria, a vaccination drive against the virus is set to be rolled out next Tuesday, the Africa CDC said.
Frontline healthcare workers and close contacts of infected patients are set to be given priority in DR Congo, which has 200,000 vaccines donated by the European Commission, it said.
Additional reporting by BBC Africa health reporter Makuochi Okafor