Amid a surge in new coronavirus cases and deaths, Africa is now suffering its worst period of the pandemic, the World Health Organization said Thursday.

The continent’s latest wave of infections is being driven in part by more contagious variants such as delta, health experts say, and is sending more young people to the hospital as countries struggle to acquire vaccine doses.

For seven consecutive weeks, cases have risen across the continent, according to WHO data. Infections climbed 20 percent in the seven days ending July 4 compared to the prior week, the agency said, adding that the African region also reported a sharp 23 percent increase in fatalities over the same period.

“Africa has just marked the continent’s most dire pandemic week ever, ” Matshidiso Moeti, WHO regional director for Africa, said in a statement. “But the worst is yet to come as the fast-moving third wave continues to gain speed and new ground.”

Here are some significant developments:

  • Pfizer will seek emergency use authorization for a booster dose to its two-shot vaccine, although U.S. health authorities also said Thursday that third doses are not needed “at this time.”
  • Japan will bar spectators from all Olympic events held in and around Tokyo as the government imposed a fresh state of emergency to cover the capital during the Games. Organizers previously capped attendance at the lower of 10,000 people or 50 percent of a venue’s capacity.
  • South Korea reported a record 1,316 new coronavirus cases on Friday, prompting the country to tighten curbs in Seoul to the highest level.
  • Brazil, which has been badly stricken by the pandemic, registered the highest number of deaths and lowest number of births in the January-to-June period since comparable data was first compiled in 2003.
  • Thailand’s recently launched sandbox program, which allows many fully inoculated travelers quarantine-free access to Phuket island, welcomed nearly 2,400 visitors in the first week of July. The rest of the country continues to struggle with high cases and a slow vaccine rollout.

Sixteen African countries are now experiencing a resurgence, including at least 10 where the delta variant has been detected. On Thursday, Nigeria announced its first confirmed delta case, detected in a traveler who the country’s Center for Disease Control said was tested on arrival.

Some of the most severe outbreaks are unfolding in countries in southern and eastern Africa, including Namibia, Uganda and Zambia. South Africa, the continent’s hardest-hit nation, recently reported the highest numbers of new infections and deaths, registering a 46 percent increase in fatalities from the virus in the week to July 4.

“The end to this precipitous rise is still weeks away,” Moeti said of the continent-wide surge. “Cases are doubling now every 18 days.”

Just over 1 percent of Africa’s roughly 1.3 billion people are fully inoculated, according to the WHO. And last month, amid a global supply crunch, shipments to the continent through the Covax initiative nearly ground to a halt.

“But there are signs of progress on vaccine deliveries,” the WHO said this week.

UNICEF, the U.N. children’s agency, announced Thursday that it signed an agreement to supply the African Union with up to 220 million doses of the single-shot Johnson & Johnson vaccine by the end of 2022.

Those doses would supplement other vaccine deliveries arriving through Covax, the U.N.-backed initiative seeking the equitable distribution of coronavirus vaccines worldwide.

Katerina Ang in Seoul contributed to this report.