The World Health Organisation says there might never be a “silver bullet” for COVID-19 despite researchers worldwide working around the clock to develop a vaccine.

WHO Director-General Tedros Adhanom Ghebreyesus acknowledged there are a number of vaccines in phase three clinical trials.

He reiterated their hope that there will, therefore, be a number of vaccines that can help prevent people from infection but said the road to normality will be long.

“There’s no silver bullet at the moment – and there might never be,” Dr Tedros told a virtual news briefing on Tuesday morning (Australian time).

Countries must continue to rigorously enforce health measures such as mask-wearing, social distancing, hand-washing and testing.

“The message to people and governments is clear: ‘Do it all’,” Dr Tedros said.

He said face masks should become a symbol of solidarity around the world.

More than 18.15 million people around the world are reported to have been infected with the disease and 690,701 have died, according to the latest figures by Johns Hopkins University.

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Dr Tedros said that, while the coronavirus was the biggest health emergency since the early 20th century, the international scramble for a vaccine was also “unprecedented”.

But he underscored uncertainties.

“There are concerns that we may not have a vaccine that may work, or its protection could be for just a few months, not more. But until we finish the clinical trials, we will not know.”

WHO emergencies head Mike Ryan said countries with high transmission rates, including Brazil and India, needed to brace for a big battle.

“The way out is long and requires a sustained commitment,” he said, calling for a “reset” of approach in some places.

The WHO officials said an advance investigation team had concluded its China mission and laid out the groundwork for further efforts to identify the origins of the virus.

The study is one of the demands made by top donor the United States which plans to leave the body next year, accusing it of being too acquiescent to China.

A larger, WHO-led team of Chinese and international experts is planned next, including in the city of Wuhan, although the timing and composition of that was unclear.

-with AAP