Spain said Tuesday it will call in the army to try to help curb the spread of the coronavirus as parts of Europe and Asia battle new surges, while data from the UN health agency suggested the pace of transmission was easing in many parts of the world.

Governments have been ramping up efforts to contain the disease, which has claimed the lives of almost 814,000 people and infected at least 23 million since late last year.

World Health Organization data said fatality and infection rates were easing in most regions, notably in the hard-hit Americas, except Southeast Asia and the eastern Mediterranean.

But a number of countries are facing new clusters.

Spain, one of the worst affected countries in Europe, is to use 2,000 soldiers who are trained in tracking to help regions identify those who have been exposed to infected people.

"We can't let the pandemic once again take control of our lives... we must take control and halt this second curve," said Prime Minister Pedro Sanchez, who described rising domestic infections as "worrying".

Thousands of miles away, South Korea ordered the closure of all schools and kindergartens in the greater Seoul region and a return to online learning.

Another 280 infections were reported on Tuesday, taking South Korea's total to almost 18,000.

'Alarming emergence of mass infections' 

South Korea's move -- coupled with Mexico's launch Monday of a nationwide televised schooling programme -- underlined the effect on young people of a pandemic now dragging into its ninth month.

"The alarming emergence of mass infections since August is turning up as infections of our students and staff members," said South Korean Education Minister Yoo Eun-hae.

UN estimates say at least 60 percent of the global student population has been impacted by school closures across more than 140 countries.

Although fatality rates have been falling, the WHO said it recorded more than 1.7 million new coronavirus cases and some 39,000 new deaths in the week to August 23.

That represented however a five-percent decrease in new cases globally and a 12-percent drop in new deaths compared with the week before.

Bolt in quarantine 

The latest high-profile case was sprint legend Usain Bolt, who was in quarantine Monday after undergoing a test for the virus that Jamaican media reported had come back positive.

The retired 100 and 200 metres world-record holder -- one of a growing number of sports personalities to fall victim to the virus -- said on Twitter that he was "trying to be responsible" by going into isolation, but he did not confirm the result.

Anxiety about the pandemic's longevity was deepened by researchers in Hong Kong revealing they had identified what they said was the first confirmed case of COVID-19 reinfection, raising questions about the durability of immunity.

The patient, a 33-year-old man living in Hong Kong, tested positive in March but after two negative tests was found to be positive again in August.

Study lead author, microbiologist Kelvin Kai-Wang To, told AFP: "COVID-19 patients should not assume after they recover that they won't get infected again."

Months of lockdowns to stem the virus spread have seen millions lose their jobs and swathes of businesses shut their doors amid fears of a second wave.

On Tuesday, Australian airline Qantas said it would cut almost 2,500 more jobs on top of 6,000 already announced, while Finnair said it would slash 1,000 posts.

Airlines have been clobbered by a collapse in tourism as nations keep their borders closed.

The race to bring a vaccine to market hotted up still further as Britain-based pharma giant AstraZeneca said it had begun a clinical trial of a drug designed both to prevent infection and treat people with COVID-19.

The drug is being tested on 48 healthy people aged between 18 and 55, the company said, hailing "an important milestone" in the fight against COVID-19.

Meanwhile, the Australian version of the global TV hit "The Masked Singer" is facing a growing cluster of cases.

Production was halted at the weekend when a dancer tested positive for the virus, its network said, forcing celebrity judge Dannii Minogue and the rest of the cast and crew into two weeks of self-isolation.