What is the basis of the UK government's coronavirus measures?

With Britain dramatically stepping up its action plan to fight the coronavirus, we explore the measures outlined by Boris Johnson on Monday and the thinking and science behind them.

Avoid all nonessential social contact and ‘unnecessary’ visits to care homes

The idea behind avoiding all unnecessary contact is simple: the fewer people you come into contact with, the fewer people can infect you, and the fewer you can infect if you are harbouring the virus. This is what social distancing is all about.

At the moment, the vast majority of the population are susceptible to coronavirus infection. Interact less, and the rate of infections will slow down. This is especially important in care homes, where people are likely to be highly dependent on others and extremely vulnerable because of their age. Fewer cases means less demand on the NHS and with that, fewer fatalities.

Avoid pubs, clubs, cinemas and theatres, and work from home

The prime minister said everyone should avoid gatherings and social meeting places, but stopped short of asking them not to open. Those who can work from home, should. Any place where people sit close together – within two metres of each other – for a period of time is a place where the virus can spread.

Coronavirus spreads primarily through airborne droplets, mostly those coughed or sneezed into the air. But the virus can also spread via tabletops, cutlery and toilet doors: it can survive on hard surfaces for several days if they are not cleaned properly.

The over-70s, pregnant women and those with health issues

Those who are aged over 70, people with underlying health conditions and pregnant women should be particularly careful, according to Prof Chris Whitty, the chief medical officer.

Coronavirus tends to be far more dangerous to older people. In China, only 0.4% of 40-somethings known to have contracted the virus died. But in those aged 80 or over, the death rate was 15%.

The reason is that with old age comes other diseases, a weaker immune system and worse overall health. The respiratory system itself is also weaker in the elderly. Underlying health conditions such as high blood pressure and diabetes are known to raise mortality risk, but the evidence is not in on pregnant women.

Last week, the Royal College of Obstetricians and Gynaecologists and others said there was no evidence the virus could pass from mother to baby. This was not the case with previous lethal coronaviruses, Sars and Mers.

12 weeks’ isolation for the most vulnerable

Johnson said that by this weekend, it will be necessary to go further to ensure that those with the most serious health conditions are shielded from social contact for about 12 weeks. He did not define the most serious health conditions on Monday. “This is going to be very disruptive for people who have such conditions, and difficult for them, but, I believe, it’s now necessary,” Johnson said.

The most vulnerable face the toughest restrictions: to reduce as far as possible all contact with others. The intention is to protect those most likely to fall seriously ill and die if they contract the infection. The 12-week period is aimed to cover the weeks when the outbreak is at its peak, whenthe highest number of people are infected.

Entire households should self-isolate for 14 days if anyone suspects they have the virus

Johnson said all members of any household which includes a single person who suffers from a dry cough or a fever should, if possible, avoid leaving the house “even to buy food or essentials”.

This is an admission by the government that if one person in a household gets infected, any others in the house are likely to contract the infection too. The entire household must self-isolate for 14 days, giving enough time not only for the first person’s infection to run its course, but any other infections that result to appear. The advice remains to self-isolate for seven days if you have coronavirus symptoms and live alone.

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Testing will be ramped up

On Monday, the head of the World Health Organization said not enough tests were being carried out. Prof Whitty defended the UK’s testing regime but said: “We do intend to continue to scale up testing.”

Scaling up testing will give scientists a clearer idea of how many infections are in the community, but Whitty was keen to promote a new test being developed by Public Health England that will detect whether people have had the infection without knowing.

That test will give a truer figure of the spread of the infection in the community and reveal how dangerous the disease is not only to those who fall ill, but to all who become infected.

The UK is “three weeks” behind Italy

Sir Patrick Vallance, the UK’s chief scientific adviser, said the disease is accelerating through the UK and the country is less than a month behind Italy, the worst-hit country in Europe, where more than 1,800 people have died.

In the early stages, epidemics tend to follow a similar pattern of exponential growth with the number of infections rising dramatically with time until the number of people left to infect falls off.

This has played out in Italy and other regions where the virus was not contained early enough. The spread is driven by transmission between people in a region rather than by imported cases.

London is the centre of the UK’s outbreak

The disease is rapidly spreading throughout the capital, and both the prime minister and Whitty urged Londoners to take particularly seriously the advice about working from home, and avoiding confined spaces.

As the main urban and financial centre of the country, and the largest transport hub, it is unsurprising that the UK outbreak is most severe in London, which has had 400 confirmed cases – nearly half the total in England.

Johnson said London appeared to be a few weeks ahead of the country in terms of the rising number of cases, suggesting that most of the infections came into and spread from the capital.

We are approaching ‘the fast growth part of the upward curve’ for coronavirus

According to the Scientific Advisory Group for Emergencies (Sage), the UK is approaching the fast growth part of the upward curve. “Without drastic action, cases could double every five or six days,” the prime minister said.

He said the number of cases had probably doubled from this time last week, when the number of actual infections was estimated at between 5,000 and 10,000.

Prof Neil Ferguson, director of the MRC Centre for Global Infectious Disease Analysis at Imperial College London, said there is uncertainty over the true figure, but added there could have been 50,000 cases in the UK so far, with about 20,000 to 25,000 infected now.

“What we’re seeing and we’ve seen for past three to four weeks as transmission got established in the UK is exponential growth. We think it’s doubling on the order of every five to six days. It will get worse from now on,” he said.

Schools remain open – for now

Vallance said further measures such as closing schools may be necessary at some point. “Those things need to be done at the right time,” he said.

Schools are remaining open for the time being, but there is concern that even though children are rarely affected by the disease, they do become infected and are almost certainly able to pass the infection on to others.

Johnson indicated that school closures my come when the timing is right. Sian Griffiths, emeritus professor at the Chinese University of Hong Kong, said this may involve closing some schools in some areas but not others. The Easter holidays are looming but may start earlier than expected at some schools.