China has reported more than 20,000 Covid-19 cases, the highest daily tally given since the start of the pandemic, as millions in locked-down Shanghai began a new round of testing.

The country's "zero-Covid" strategy has come under immense strain as cases spike, with around 25 million residents of Shanghai - China's largest city and economic engine room - ordered to stay-at-home as the authorities struggle to contain the outbreak.

The number of infections recorded hit 20,472 infections today, the National Health Commission said in a statement.

It is the country's highest-ever daily infection number given by authorities, even during the peak of the initial outbreak which centred around Wuhan.

The majority of the cases are, however, asymptomatic.

Until March, China had kept daily cases low with snap localised lockdowns, mass testing, and strict restrictions on international travel.

But the caseload has hit thousands per day in recent weeks, with Shanghai accounting for more than 80% of the national tally, city officials said today.

The city locked down its residents in phases last week, prompting scenes of panic-buying and mass testing.

But state broadcaster CCTV reported that the city will launch a fresh round of tests on the entire population on Wednesday.

Shanghai is "testing its strength against the virus," senior city health official Wu Qianyu said at a press conference today, the latest dour warning from authorities suggesting a long run in lockdown may be ahead.

The city is converting its landmark National Exhibition and Convention Center into a makeshift Covid hospital for 40,000 people, state news agency Xinhua reported today, just days after setting up a temporary quarantine centre in another expo hall.

The National Exhibition and Convention Center in Shanghai

In Shanghai, quarantine facilities are bulging with people who test positive - even if they are asymptomatic - as city officials stick rigidly to virus protocols.

Those include separating Covid-positive babies and children from parents who test negative, a policy that has stirred anxiety and anguish from worried families.

City officials said today that parents of some child patients with "special needs" would now be allowed to remain with their Covid-positive children.

Meanwhile, anger over lack of fresh food and curtailed movements is rising among residents as officials extend what was originally intended to be a short lockdown.

A top Shanghai official has conceded that the financial hub had been "insufficiently prepared" for the outbreak.

China, the country where the coronavirus was first detected in the central city of Wuhan in late 2019, is among the last remaining places following a zero-Covid approach to the pandemic.

The outbreak has taken on an increasingly serious economic dimension, with China's factory output falling to its lowest in two years in March and services activity suffering a "notable drop in sales," according to independent indices released by Chinese media group Caixin.

Germany drops plan to relax Covid quarantine rules

Germany will not end mandatory quarantine for most people who catch Covid-19 after all, the health minister said today, reversing course after concern was raised that lifting quarantine restrictions would drive even higher infections.

"Coronavirus is not a cold. That is why there must continue to be isolation after an infection," Health Minister Karl Lauterbach said on Twitter, adding he had made a mistake by suggesting an end to mandatory quarantine.

Under the existing rules, people with Covid must quarantine for at least seven days.

A sign asking people to continue to wear a face mask is seen hanging
in front of an electronic retailer in the German city of Cologne

Mr Lauterbach suggested last week a shift to a voluntary five days of self-isolation with the recommendation of a Covid test at the end of that period.

The idea of ending quarantine, except for medical staff, had emerged after Covid cases soared in recent weeks, hitting staffing in hospitals and many other workplaces.

Daily infections have fallen in the last week or so, with 214,985 new infections reported today, about 20% fewer than a week ago. That took total cases since the pandemic began beyond 22 million, with 130,708 deaths.

Germany has been discussing making vaccinations mandatory although support for the idea has waned as the Omicron variant has led to fewer cases of severe illness, with only those over 60 likely to be compelled to get a shot from October.

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Second booster shields elderly from Covid but protection wanes quickly - study

A fourth dose of the Pfizer/BioNTech vaccine lowered rates of Covid-19 among the elderly, but the protection against infection appeared short-lived, a large study in Israel has found.

The second booster's protection against infection dwindled after four weeks, Israeli researchers showed in their study published yesterday in the New England Journal of Medicine.

Protection against severe illness did not wane during the six weeks after the dose but more follow-up study was needed to evaluate its longer-term protection, the researchers said.

The study on 1.3 million people aged 60 and older looked at data from the Israeli Ministry of Health database between 10 January and 2 March, when the Omicron variant was predominant.

It comes ahead of a meeting by the US Food and Drug Administration today to discuss the need for additional boosters, a week after the United States authorised a second booster shot for people aged 50 and older amid a spread of the Omicron sub-variant BA.2.

European health ministers have also urged the bloc's governments to back a fourth dose for people over 60.

In Asia, South Korea started giving out fourth doses of Covid-19 vaccines in February and Singapore has said a second booster dose is planned for those aged 80 and older.

Another study from Israel showed last month that seniors who received a second booster of the Pfizer Inc/BioNTech vaccine had a 78% lower mortality rate than those who got just one.

Israel started offering a second booster in January.