WHO director-general Tedros Adhanom Ghebreyesus has also said he was "appalled" by comments by a leading association of pharmaceutical manufacturers a day earlier that said vaccine supplies were high enough to allow for both booster shots and vaccinations in countries in dire need of jabs but facing shortages.

"I will not stay silent when companies and countries that control the global supply of vaccines think the world's poor should be satisfied with leftovers," he said in Geneva on Wednesday.

Tedros had previously called for a "moratorium" on booster shots through the end of September. But wealthy nations countries - including Israel, Britain, Denmark, France, Germany, Spain and the US - have begun or are considering plans to offer third shots of two-dose vaccines to their vulnerable people such as the elderly or those with compromised immune systems.

The WHO chief said he received "clear support" at a meeting of G20 countries this month for a WHO target that all countries vaccinate at least 40 per cent of their people by year's end.

"A month ago, I called for a global moratorium on booster doses, at least until the end of September to prioritise vaccinating the most at risk people around the world who are yet to receive their first dose," Tedros said.

"There has been little change in the global situation since then.

"So today, I'm calling for an extension of the moratorium until at least the end of the year to enable every country to vaccinate at least 40 per cent of its population."

WHO says 5.5 billion coronavirus vaccines have been administered so far, but 80 per cent of those have been to upper- and middle-income countries.

Tedros said rich countries had offered to donate one billion vaccine doses but under 15 per cent of those doses had "materialised".

Australian Associated Press