Africa is experiencing its fastest surge in COVID-19 cases this year, with the number up 83% in the past week, though deaths remain low, the World Health Organisation (WHO) said on Tuesday.

The spike in cases is driven by the Delta and Omicron variants, the WHO said in a statement. The number of new COVID-19 cases on the continent is currently doubling every five days, the shortest time frame reported this year.

Africa's low inoculation rates have encouraged viral mutations like the new Omicron variant to spread, according to health experts. The continent struggled to obtain vaccine doses until recently, and is facing challenges to distribute them including lack of funds, staff and equipment.

As of Monday, only 20 African countries had vaccinated at least 10% of their population, according to the WHO. Some countries, like Democratic Republic of the Congo and Chad, have vaccinated less than 1%, data collected by Reuters shows.

“We are cautiously optimistic that deaths and severe illness will remain low in the current wave, but slow vaccine rollout in Africa means both will be much higher than they should be,” said Dr. Matshidiso Moeti, WHO Regional Director for Africa.

Africa recorded more than 196,000 new cases for the week ending on Dec. 12, up from around 107,000 the previous week, the WHO said. Deaths dropped by 19% in the same period, it said, and have averaged about 1,000 per week in the fourth pandemic wave.

At the current pace, it will take until May 2022 before Africa reaches 40% vaccination coverage and August 2024 before it reaches 70%, the WHO said.