The virus is still spreading rapidly worldwide, with over one million deaths and 37 million infections, and many nations that suppressed their first outbreaks now face a second wave.

Without a vaccine, governments are wary of allowing the virus to spread unchecked.

China -- where Covid-19 first emerged late last year -- launched a drive to test all residents of Qingdao after a handful of cases were detected on Sunday.

More than four million samples had been collected and 1.9 million results returned as of Tuesday afternoon, Qingdao authorities said, adding that no new cases had been found beyond already confirmed infections.

Chinese officials intend to test the entire city -- around 9.4 million people -- by Thursday.

In scenes contrasting with the fumbled testing efforts elsewhere, health workers in protective clothing swiftly set up tents and residents queued deep into Monday night to provide samples.

In Europe, governments are battling to curb surges with new controls and increased testing, while trying to avoid the devastating nationwide lockdowns of March and April.

Cases have climbed rapidly in Britain, France, Germany, Poland, and the Czech Republic in recent weeks, raising fears that the death rate could rise.

Hospitals in Paris will have most of their intensive care beds packed with Covid-19 patients as soon as next week, the system's chief warned Tuesday.

"It's inevitable," Martin Hirsch, the head of the 39 hospitals in Paris and its suburbs, told the Parisien newspaper, estimating beds would reach 70-90% capacity by October 24.

President Emmanuel Macron is widely expected to announce tighter restrictions in a prime-time TV interview Wednesday night, with some media speculating Paris and other cities could face evening curfews.

Russia on Tuesday reported its highest-ever number of daily virus deaths, at 244, and a record number of new cases at almost 14,000.

Italy imposed new, tougher rules to control a resurgence, including an end to parties, amateur football matches and snacking at bars at night.

Polish Prime Minister Mateusz Morawiecki on Tuesday became the latest high-profile figure to go into quarantine after coming into contact with a person with Covid-19.

And Portugal's football federation said star striker Cristiano Ronaldo had tested positive for the virus.

Britain's Prime Minister Boris Johnson, whose country has the highest death toll in Europe, on Monday had already ordered pubs in Liverpool to shut as part of a new strategy.

He said businesses forced to close would get support from the government, but his focus on shutting hospitality venues sparked anger, as have similar measures elsewhere.

"Catastrophic, catastrophic," said Simon Ashdown, owner of the Chepstow Castle pub in Liverpool. "I don't think there'll be many businesses after this lockdown."

- 'Ethically problematic' -

In opposition to lockdowns and social distancing, some politicians have proposed letting the coronavirus circulate in the population to build up "herd immunity" -- where so much of the population has been infected there are insufficient new victims for the virus to jump to.

But the World Health Organization dismissed such plans as unworkable, requiring mass vaccinations to work.

"Herd immunity is achieved by protecting people from a virus, not by exposing them to it," WHO chief Tedros Adhanom Ghebreyesus said, describing the idea as "scientifically and ethically problematic.

"Allowing a dangerous virus that we don't fully understand to run free is simply unethical. It's not an option."

Underlining the challenge, a study published in The Lancet Infectious Diseases journal indicated that exposure to the virus may not guarantee future immunity -- and the second infection could come with even more severe symptoms.

- Vaccine setback -

With the pandemic already claiming more than one million lives worldwide, scientists in different nations are rushing to develop vaccines and effective treatments.

Some have made it to late-stage clinical testing, but the optimism was dented Monday when Johnson & Johnson announced it had temporarily halted its 60,000-patient trial because of an unexplained illness in one participant.

They are one of 10 firms conducting final Phase 3 trials of their products globally.

The pharma giant has been awarded about $1.45 billion in US funding under Operation Warp Speed, championed by President Donald Trump, who is keen for a political boost ahead of the November election with a coronavirus breakthrough.

Critics have excoriated Trump for his handling of the crisis, with more known infections and deaths in the United States than anywhere else in the world.

Trump was sidelined from the campaign trail for 10 days after he got Covid-19, but returned to the stage Monday.

"I went through it and now they say I'm immune... I feel so powerful," Trump told a cheering crowd in Florida, few of whom wore masks.

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JOHNSON & JOHNSON