GENEVA — The head of the World Health Organization said that over 87% of the more than 700 million doses of coronavirus vaccine that have been administered worldwide have been given in wealthier countries.

WHO Director-General Tedros Adhanom Ghebreyesus said that on average, one in four people in rich countries have received at least one dose of a COVID-19 vaccine, compared to only one in 500 people in low-income countries.

“There remains a shocking imbalance in the global distribution of vaccines,” Tedros said during a media briefing Friday.

He called COVAX, the U.N.-backed initiative to distribute vaccines fairly, “a strong mechanism that can deliver vaccines faster and more efficiently than any other mechanism.” He noted that COVAX so far has delivered about 38 million doses worldwide, or enough to cover about 0.25% of the global population.

Tedros criticized countries that plan to donate vaccines directly to other nations instead of going through COVAX.

“These bilateral arrangements run the risk of fanning the flames of vaccine inequity,” he said, without explaining why donations that bypass COVAX were problematic.