When will the UK lockdown end? The four exit strategies

Britain's coronavirus epidemic is expected to peak in around three weeks before a steady decline in deaths. But will that mean an end to social distancing, or could we be facing a lockdown until the end of the year?

Here are the most likely scenarios:

1. Intermittent social distancing

All scenarios involve waiting until the virus has peaked and the number of deaths has started to fall dramatically before any action will be taken.

If our timeline mirrors China, the Government could be in a position to consider lifting restrictions by early summer.

Under the first strategy, some social distancing and lockdown measures would continue throughout much of the year, but there would be breaks in which life would get back to normal.

For example, social distancing could be alternated on a regional basis to give people a rest from draconian restrictions.

The Scientific Pandemic Influenza Group on Modelling, which feeds into the Scientific Advisory Group for Emergencies (Sage), has proposed that parts of the country could enjoy greater freedoms for six months at a time, before returning to lockdown.

Several apps have recently come online, tracking symptoms throughout the country, which could give public health officials an idea about where hotspots are, so they can be locked down early. Lockdown may also be re-established as we move towards the winter months and the NHS finds itself under increased pressure.

Paul Hunter, Professor of Medicine at the University of East Anglia said: "Personally, I suspect that the disease will tail off during June and July, partly because of social distancing, partly because of increased population (herd) immunity, and partly because these sorts of infections tend to spread less readily during the summer.

"So I suspect there will be some relaxation at that time. But I think it may come back, though less aggressively, in the autumn, and social isolation may need to be strengthened for a while."

A fragmentary, regional lockdown would give the NHS a series of breaks, allowing it to ramp up capacity and then enjoy quieter periods.

And it would allow time for a vaccine or treatment to be created and for immunity in the population to build up slowly.

Mark Woolhouse, Professor of Infectious Disease Epidemiology at the University of Edinburgh, said: "It's almost certain to be a partial release. Whatever measures are relaxed, that runs the risk that the epidemic curve will start to increase again.

“Extending the lockdown buys you more time to raise the capacity in the NHS. That wouldn't solve the epidemic problems, and you would need to be in another lockdown eventually - but it would give us longer.”

2. Allow the healthy and immune out

Shielding the vulnerable, and allowing the healthy or immune out to carry on with their lives and get back to work, could be a way to break the deadlock and allow major parts of society to return to normal.

The Government has promised that antibody tests - which show whether someone has had the virus and is now immune - will be available within weeks, and Britons could soon be issued "immunity certificates" that would allow them to leave the lockdown.

In the coming weeks, public health experts are also due to start community surveillance to find out how many people have had the virus, which could end the need for a lockdown.

Prof Hunter added: "If a large proportion - somewhere around 60 per cent - of the population become immune,  the lockdown will not serve that much more purpose as herd immunity will be at a level that the disease would struggle to spread. So, lockdown over.

"One thing that may happen, is that people who can prove that they had the infection and are now immune may be allowed more access to work, etc.

"If social distancing has worked and the NHS has survived then, we are likely to see a much smaller proportion of the population being immune. The risk of relaxing too early is that you then get a second peak.

"However, subsequent peaks will usually be less dramatic and potentially more manageable."

Under this scenario, the Government could also bring in weekly testing for people most at risk of spreading the disease, such as doctors, nurses, supermarket workers and delivery staff.

Prof Woolhouse said: "We could change tack slightly. At the moment the emphasis is very much on reducing transmission in the community, but if shielding the vulnerable could be enhanced including very rigorous testing with infected persons being isolated then that will save lives.

"It will also reduce the burden on the NHS and it will also allow the rest of us to be released from some of the measures."

Germany, which is carrying out hundreds of thousands of tests, is planning to give certificates to citizens.

Prof Karol Sikora, Dean of Medicine at the University of Buckingham said: "Germany has got testing spot-on.

"They plan to test hundreds of thousands for the presence of the antibodies and issue 'immunity certificates' to those who test positive, allowing their work to be exempt from the lockdown. This information will be a huge weapon against the virus."

3. Seek and destroy

This strategy involves waiting until the virus is at a very low level, lifting restrictions and combating the remaining cases through aggressive contact tracing, testing, isolation, and precision quarantine zones.

The method has been adopted successfully in Singapore and South Korea, which have coped far better than most other countries, and have done so without major lockdowns.

Jeremy Hunt, the former Health Secretary and Chairman of the Health Select Committee, said such a strategy could save months of "anguish and economic strife".

"If you look at what's happening in South Korea and Singapore, they've managed to keep their offices, shops, restaurants open, but they do that by having a mass programme of testing so anyone with symptoms is tested, everyone they’ve come into contact with is tested, and you can keep on top of the virus.

"So when we get through this and we want to avoid these kinds of lockdowns again, and keep the economy going,  mass testing is the way to do it."

Mr Hunt said Britain was in the enviable position of being able to look at the policies of other countries to see what's working, and said Government modellers were keeping a close eye on Wuhan, the Chinese city where the global pandemic began, to see if the virus reemerges following the lifting of social-distancing restrictions.

Prof Woolhouse added: "The third strategy, is essentially to extend the lockdown until numbers are very low indeed and try and implement a 'seek and destroy mission' where you try and track down every single case, testing very extensively and isolating those infected. But you can only do that if the numbers are not that high."

Dr Marc Lipsitch, Director and Professor of Epidemiology at  Harvard University, published a paper last week suggesting that once testing is scaled up on a bigger scale, restrictions could be lessened.

"If the case numbers are really low enough, you can do a more Singapore-like strategy of following individual cases rather than just social distancing," he said.

"Aggressive contact tracing and quarantine - impractical now in many places but more practical once case numbers have been reduced and testing scaled up - could alleviate the need for stringent social distancing to maintain control of the epidemic."

A new open-source app from Massachusetts Institute of Technology called Private Kit: Safe Paths notifies users if someone they have been in close contact with has tested positive so they can self-isolate. Some countries are using CCTV to trace who infected people have been near so they can be traced.

4. Wait for vaccine or treatment

The final option is to wait it out until a vaccine or treatment is available and then build up herd immunity. Many scientists think that is the only long-term solution to getting life back to normal.

Earlier this month, Prof Neil Ferguson, the key epidemiologist advising the Government, said: "The only exit strategy from this long term is vaccination or some other kind of innovative technology."

Scientists have predicted that the first vaccines will not be available until the end of the year at the earliest, and even then, they will be reserved for frontline workers and the most vulnerable in the first instance.

Treatments could be quicker, with dozens of trials under way to see if antivirals that are already used for other conditions, such as malaria and HIV, could prove effective. Plasma from the blood of recovered victims could also be injected into patients.

If a working cure does become available in the coming weeks or month then lockdown will be lifted far sooner.

Prof Hunter added: "By autumn we may have some proven effective drug treatments that if taken early enough could reduce the severity of illness and need for hospitalisation, critical care beds and ventilatory support.

"If that is the case then that would also be a reason for relaxing social distancing."