GENEVA: The WHO wrote to every country on Tuesday urging them to quickly join its global shared vaccine programme - and spelled out who would get its eventual coronavirus jabs first.

The World Health Organization's director-general Tedros Adhanom Ghebreyesus said that without vaccinating the planet's highest-risk populations simultaneously, it would be impossible to rebuild the global economy.

And he said the most exposed 20 percent of each country's population - including front-line health workers, adults over 65 and those with pre-existing conditions - would be targeted in the first wave of vaccinations, once the WHO-led COVAX shared facility can roll out a proven safe and effective vaccine.

"The fastest way to end this pandemic and to reopen economies is to start by protecting the highest risk populations everywhere, rather than the entire populations of just some countries," Tedros told a virtual press conference.

The novel coronavirus has killed nearly 775,000 people and infected almost 22 million since the outbreak emerged in China last December, according to a tally from official sources compiled by AFP.

Researchers and pharmaceutical giants are racing to produce a vaccine, with nine of the 29 currently being tested on humans forming part of the COVAX Global Vaccines Facility.

"If there's a winner in vaccines, we'll have one, there's absolutely no question," said WHO advisor Bruce Aylward.

Some 92 countries are signed up to COVAX - an effort to pool the costs and rewards of finding, producing and distributing effective vaccines - while a further 80 have expressed interest but are yet to commit fully.

The WHO wants countries to signal a firm interest by August 31.