Repeat testing of everyone in city of half a million people is ambitious to say the least. But is it achievable and if it is, what is it supposed to achieve?
Apart from a full lockdown, mass testing is perhaps the most powerful tool you can use against Covid-19.
As many as 50% of people infected with SARS-CoV-2 show no symptoms at all, and we now know for those who do get symptoms they are most infectious before those symptoms show.
It’s one of the reasons our current Test and Trace system would struggle to contain the virus even if it was working properly.
Mass testing - inviting everyone for a test - gets around that problem. In theory, you’ll pick up all infections whether symptomatic or not.
If they all then isolate within a couple of weeks, you could eradicate the virus in the population you’ve tested.
We should have the testing capacity. The government says it has achieved its target capacity of 500,000 tests a day.
With a lockdown coming in soon in England, demand for testing should hopefully start to reduce in the coming days.
They also promise to use new "moonshot" testing technologies in the Liverpool trial including pregnancy test-style "lateral flow" kits that can give a result instantly without the need for a lab.
And the government has also called the army in to help with logistics.
But it isn’t organising testing that’s the main challenge. It’s organising the people.
The plan only works if everyone who can comes forward for testing.
Even if, as is rumoured, the isolation period is cut from 14 to 7 days, how many people in Liverpool will be willing to volunteer for testing?
It’s a big ask for someone who has no symptoms and is trying to make a living in lockdown.
Then there’s persuading people to isolate. In the UK, the existing test and trace system has failed to provide data on people’s compliance with isolating, but even the prime minster has indicated it’s not good enough.
Successful test and trace systems like those in South Korea and Vietnam rely on rigorous compliance with contact tracing and isolation.
Once asked to isolate, cases get a call as often as once a day to check in on them. A lot of contact tracing and follow up is done door-to-door by local health teams.
This isn’t happening at scale in the UK and there’s no mention in today’s announcement from the government about whether it will be.
It’s also not clear whether trialling such a system during a full lockdown will give the right answers. Everyone is supposed to be isolating during lockdown anyway.
If the long-term strategy for mass testing is for a post-lockdown safety net that keeps the virus in check, it could be a hugely powerful took to allow local areas to contain hotspots of infection.
But to ensure any such system isn’t just chasing the virus around the country, infection rates across the UK would have to be much, much lower than they are right now.
Otherwise it is almost impossible to see how there could be the capacity - both technological and human - to regularly test all 67 million of us and ensure we all isolate as patience with this pandemic wears thin.