There is a simple but crucial number at the heart of understanding the threat posed by the coronavirus. It is guiding governments around the world on the actions needed to save lives and to lift lockdown.

It is called the reproduction number, or simply the R value. But what is it?

The reproduction number is a way of rating a disease's ability to spread.

It's the number of people that one infected person will pass the virus on to, on average.

BBC News presenters of South Asian origin have united in a campaign to share vital coronavirus advice in seven different languages for the British Asian community.

Check out the video below.

Yogita Limaye
BBC India correspondent

India and Bangladesh are evacuating millions of people from coastal areas ahead of a super cyclone, which is approaching from the Bay of Bengal.

Two Indian states - West Bengal and Odisha - are expected to be hit by Cyclone Amphan, along with parts of Bangladesh. It is forecast to make landfall in an area near the border of the two countries on Wednesday.

While both countries have a lot of experience dealing with cyclones that develop every year in the Bay of Bengal, the coronavirus outbreak is making the challenge of evacuating people harder this time.

Extra shelters have been prepared to allow for social distancing. Masks are also being distributed.

Read more

Image source, Getty Images

The management of K-pop boy band BTS has apologised after one member of the group went to a bar last month, ignoring government advice.

Jungkook visited a bar and restaurant in the Itaewon neighbourhood of Seoul on 25 April. Such establishments were permitted to open during this period but strict social distancing measures were required and the government had advised people to steer clear of them completely.

There was an outbreak of Covid-19 in the same area after lockdown measures were relaxed earlier this month.

“We have no excuse that we placed the artist’s personal life before we were able to emphasise the importance of social distancing. We bow our head in apology,” Big Hit Entertainment said.

“He is also deeply regretting on how he did not follow social distancing measures seriously.”

The star has since tested negative for the virus.

Robert Cuffe
BBC head of statistics

The numbers of deaths in care homes have fallen for the second week in a row, figures from the Office for National Statistics show.

In the week up to 8 May, there were 1,666 Covid-19 registered deaths in care homes in England and Wales. This is down from 2,423 the previous week.

The fall is exaggerated by the pause in death registrations on the Bank Holiday Friday, but is larger than would be caused by a single day of closures.

The number of deaths in care homes in England and Wales also fell from 6,409 to 4,248.

Read more on the care homes figures.

Reality Check

Image source, Getty Images

President Trump has said he’s been taking hydroxychloroquine, a drug normally used to treat malaria, as a preventative measure against coronavirus.

Mr Trump first touted anti-malarial drugs in late March, causing a global surge in demand for the treatment most commonly used in developing countries. Prescriptions in the US have also soared.

The WHO says there is no definitive evidence it works against Covid-19 and that it’s concerned by reports of individuals self-medicating and causing themselves serious harm.

The Food and Drug Agency (FDA) warned in April of serious side effects, such as heart problems, and advised against its use outside of a hospital setting or clinical trials.

Many countries are conducting studies on the effectiveness of anti-malarial drugs against the virus.

See here for more on Covid-19 and hydroxychloroquine.

A letter from Donald Trump criticising the World Health Organization's response to the coronavirus is inaccurate, says the editor of a medical report cited by the US president.

Mr Trump sent a letter to the head of the WHO threatening to pull US funding and outlining a 30-day deadline for the body to commit to "substantive improvements".

In it, Mr Trump says the WHO "consistently ignored reports of the virus spreading in Wuhan in early December 2019 or even earlier, including reports from the Lancet medical journal".

However, editor Richard Horton says The Lancet did not publish any report until 24 January.

In a tweet, he wrote: "Dear President Trump - You cite The Lancet in your attack on WHO. Please let me correct the record. The Lancet did not publish any report in early December, 2019, about a virus spreading in Wuhan. The first reports we published were from Chinese scientists on Jan 24, 2020."

Stephen McDonell
BBC News, China correspondent

The diplomatic row between China and the United States over the role of the World Health Organisation continues to escalate.

China’s foreign ministry has accused the Trump administration of attacking the United Nations body as a means of diverting attention from its own mishandling of the coronavirus crisis.

The US president has threatened to withdraw from the WHO if it doesn’t alter its operations within 30 days. Donald Trump said the organisation had shown an “alarming lack of independence” from China.

In Beijing, foreign ministry spokesman Zhao Lijian told a regular press briefing that the US was trying to smear China in order to avoid its own responsibilities.

Michelle Roberts
Health editor, BBC News online

Image source, Getty Images

For the first time, people in England are being advised to wear face coverings in some enclosed spaces.

The Scottish government already recommends people wear them when in shops and on public transport.

Wearing a face covering can prevent an infected person passing on the virus, rather than stopping someone contracting it.

The government for England says:

• People should aim to wear face coverings on public transport and in some shops
• Also in other "enclosed spaces where social distancing is not always possible and they come into contact with others that they do not normally meet"
• "Social distancing" means staying more than two metres away from someone
• Face coverings should be worn and not surgical masks or respirators, which should be left for healthcare staff and other workers who need them

See here for more information on who needs to wear masks, where you should wear them and how to make them.

Image source, Getty Images

With a planned relaxation of UK lockdown rules allowing some non-essential stores to reopen next month, major brands such as Marks and Spencer and Next are preparing for socially distanced shopping.

But analyst Richard Lim of Retail Economics said stores would "have to discount heavily" to sell excess stock that may now be out of season.

Mr Lim said retailers also faced big challenges in winning shoppers' confidence, with changing rooms likely to stay closed and customers discouraged from touching the merchandise.

"The retail experience is going to be turned on its head when clothes stores reopen," he said.

Read the full story

The Prince of Wales has urged British citizens to come together to join the Pick for Britain campaign, which calls on people to help farmers harvest fruits and vegetables.

Prince Charles likened the movement to the Land Army, which saw women work in agriculture so that men could join the military during World War Two.

"Many thousands of people will be needed to pick the crops. It will be hard graft but hugely important," Prince Charles said, in a video message that was posted to his official Instagram account.

Pick for Britain is a UK government initiative designed to help farmers who fear that Covid-related travel restrictions will cause a shortage of migrant labour to harvest crops.

Former Prime Minister Gordon Brown told ITV's Good Morning Britain that coronavirus testing in the UK was "not good enough" and that only about 3% of the public had been tested.

He said the country needed a “mass mobilisation of resources", comparable to the wartime effort to construct aircraft, to increase testing capacity and avoid a second wave of Covid-19.

“Instead of ‘stay alert’ the government’s slogan should have been ‘get tested’,” he said.

James Gallagher
Health and science correspondent, BBC News

Image source, Getty Images

More than 1.7 million people around the world are known to have recovered from coronavirus, according to Johns Hopkins University. But the road back to full health is not the same for everyone.

Recovery time will depend on how sick you became in the first place. Some people will shrug off the illness quickly, but for others it could leave lasting problems.

Age, gender and other health issues all increase the risk of becoming more seriously ill from Covid-19.

See here for more on how long Covid-19 recovery can take.

Afghan journalist and refugee Reza Adib is locked down in a migrant camp in Greece and has been investigating conditions there during the virus crisis.

Early action by the Greek government has kept infection rates low, and there have been no deaths in the camps. But fear of the virus has had a profound impact..

Image source, Getty Images

The coronavirus pandemic has led to a collapse in car sales across the European Union. In April only around 271,000 new cars were registered, 76% fewer than in the same month last year.

That's according to the European Automobile Manufacturers' Association, external (ACEA), which represents all of the major car makers in the bloc's market.

Across the first four months of the year, new registrations fell by 38.5%. The ACEA puts the sharp fall down to both manufacturing drawing to a halt and dealerships being closed for weeks.

Maddy Savage
BBC News, Stockholm

Image source, Getty Images

Lili Perspolisi's father, Reza Sedghi, was not seen by a doctor on the day he died from coronavirus, at his care home in northern Stockholm.

A nurse told her he'd had a morphine shot in the hours before he passed away, but he was not given oxygen, nor did staff call an ambulance. "No-one was there and he died alone," says Ms Perspolisi. "It's so unfair."

Most of the 3,698 people who have died from coronavirus in Sweden so far have been over 70, despite the fact that the country said shielding risk groups was its top priority.

Sweden did ban visits to care homes on 31 March. But as in many European countries, relatives, staff and union officials have shared concerns that protective clothing arrived too late, and that some staff may have gone to work at the start of the crisis, despite showing symptoms of Covid-19.

Read more here.

US President Trump has now levelled some pretty strong charges against the World Health Organization, accusing them in a four-page letter of an "alarming lack of independence from China".

But this isn't the first time he's attacked the WHO. Our Reality Check team took a look into some of Trump's previous claims to find out if there was any truth to them:

• "One of the most dangerous decisions... from the WHO was... to oppose travel restrictions. They actually fought us": The US restricted travel from China and other countries from 2 February. But there is no record of the WHO publicly criticising this move. It had, however, on 10 January put out advice recommending no international travel restrictions in response to the virus
• "The WHO [is] largely funded by the US, yet is very China-centric": The US is one of the biggest contributors to the WHO, accounting for just under 15% of its funding last year. But the Bill and Melinda Gates Foundation is also a major contributor, as are the UK and Germany

Read more about Trump's claims here.

BBC Breakfast

Earlier, Work and Pensions Secretary Therese Coffey was on BBC Breakfast responding to the huge rise in unemployment claims.

Asked if the system could cope with the demand from people asking for support, she said: "Yes."

“Meantime, the department is also working across government on what we can do to help people get back into the labour market once the economy properly recovers,” she added.

Resty Woro Yuniar
BBC News, Jakarta

Image source, Getty Images

Jakarta police say they forced nearly 20,000 vehicles to turn back as migrant workers tried to return to their hometowns, defying a ban on that type of travel, known as mudik.

While the ban has been implemented since last month, the government recently reopened domestic transport but with limitations in place.

Eid, which falls on 24 May this year, is a major holiday in Indonesia, the world’s most populous Muslim-majority nation. Here, mudik travel would typically peak in the week prior to Eid.

Despite the ban, some people have still been finding ways to return to their villages and hometowns by hiding in the baggage store of a bus or under a truck.

In the past 24 days, Jakarta police officers, who have has set up checkpoints around the city, have forced 19,940 vehicles to return to the capital. This is an increase from more than 16,000 vehicles it recorded on May 10. Across Indonesia, more than 48,000 vehicles had been turned back at the borders of various provinces in Sumatra and Java.

Inter-island travel via sea ports is also on the rise. On Sunday night, 861 travellers managed to cross from Sumatra to Java, and they were escorted by authorities to their destinations in Java by buses, for free.

Indonesia had confirmed 18,010 Covid-19 cases and 1,191 virus-linked deaths as of Monday.

Muslims around the world are observing Ramadan, when they fast during daylight hours - but how are sport's big names getting on with it during lockdown?

The global restrictions have touched everyone in some capacity, and Muslims in the UK have had to deal with both staying away from food and drink for 18 hours and mosques closing their doors.

Our colleague Shamoon Hafez hosted a Zoom call with dual-code New Zealand rugby international Sonny Bill Williams, England cricketer Adil Rashid and footballer Muhamed Besic - on loan at Sheffield United from Everton - to find out how they have been coping.