Scientists around the world are watching how the coronavirus outbreak in China develops in the coming days and weeks because it will reveal whether their modelling on how long restrictions to normal life will have to last is correct.
Yesterday scientists from Imperial College London released their detailed modelling of the coronavirus pandemic, which dramatically concluded that the UK could face an indefinite period of lockdown without a vaccine. It showed the coronavirus would return and overwhelm health services every time restrictions are lifted.
China and South Korea are two countries where severe measures on normal life have been taken to restrict the spread of the virus.
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The Imperial College experts, whose work triggered the dramatic shift in UK government tactics yesterday, said the next few weeks in China will be crucial in seeing whether the virus will bounce back.
Professor Azra Ghani, professor of infectious disease epidemiology, said: We will be learning from other countries. Were not the only country to be facing this, every country in the world is facing exactly the same challenges. Were monitoring now very closely the situation in China.
They are pursuing exactly this strategy, they have reduced transmission to very low levels, certainly below our thresholds, and now they are starting to open up their society again and we will see what happens in the coming weeks.
The challenge posed by coronavirus
According to the Imperial College study the only chance for the UK to avoid the predicted 510,000 deaths that would be caused without any action was for the country to impose restrictions on peoples movement and social contacts.
The report released yesterday showed that even with some measures of isolation and quarantining of patients, without mass restrictions on society as a whole, there were still likely to be 260,000 deaths and eight times the demand for intensive care beds, which would overwhelm the NHS.
It was this bleak assessment that prompted Boris Johnson and the UK government yesterday to set out what the prime minister accepted were pretty draconian measures.
The Imperial study on coronavirus made the risks clear: The public health threat it represents is the most serious seen in a respiratory virus since the 1918 influenza pandemic.
We show that in the UK and US context, suppression will minimally require a combination of social distancing of the entire population, home isolation of cases and household quarantine of their family members. This may need to be supplemented by school and university closures, though it should be recognised that such closures may have negative impacts on health systems due to increased absenteeism [of staff].
The future outlook for the pandemic
The problem with suppressing the spread of the virus completely is that it has a huge social and economic impact. As many as 1 million people may lose their jobs because of the fall in revenue from people not going out and spending their money.
So realistically no government can keep such measures in place forever and this is where the Imperial College report becomes even more worrying.
It shows that where social distancing measures are put in place and then relaxed the virus re-emerges.
Modelling by Imperial College shows that despite restrictions on peoples movement and daily life, when the measures are relaxed the coronavirus returns and peaks in the winter (Imperial College)
The report said: The major challenge of suppression is that this type of intensive intervention package, or something equivalently effective at reducing transmission, will need to be maintained until a vaccine becomes available (potentially 18 months or more) given we predict that transmission will quickly rebound if interventions are relaxed.
Looking at the detail the scientists show that if restrictions are in place for five months from April to September the virus will emerge again in October and peak again in November or December a period of time when seasonal flu and cold weather typically causes a winter crisis in the health service.
The more successful a strategy is at temporary suppression, the larger the later epidemic is predicted to be in the absence of vaccination, due to lesser build-up of herd immunity, the report warns.
This poses a real challenge to the government should no vaccine emerge in time for this second surge.
The on-off solution
The scientists offer one alternative option for ministers which is to activate and deactivate the restrictions to try and limit the viruss impact. 
Using a simulation where restrictions are triggered once hospitals report 200 intensive care patients a week, the scientists showed the UK could be trapped in a coronavirus cycle that could continue for two years to November 2021.
An illustration of the on-off cycle of coronavirus to November 2021 where rising cases of intensive care trigger social distancing restrictions across society. Each time the restrictions are lifted the simulation shows the virus returns (Imperial College)
The only real salvation will be the development of a vaccine but while a number of drug companies are testing candidate vaccines there is no guarantee at this stage such a vaccine will work.
This is why China and South Korea are so important and are being watched so closely. If the number of infections start to rise in both countries once restrictions are lifted that suggests the modelling predictions are right and the UK should expect a second surge as soon as normal life resumes.
The report said: While experience in China and now South Korea show that suppression is possible in the short term, it remains to be seen whether it is possible long-term.
Results in this paper have informed policymaking in the UK and other countries in the last weeks. However, we emphasise that it is not at all certain that suppression will succeed long term; no public health intervention with such disruptive effects on society has been previously attempted for such a long duration of time. How populations and societies will respond remains unclear.