COVID testing all of Liverpool

How to test a whole city?
10 November 2020

Interview with 

Julian Peto, London School of Hygiene and Tropical Medicine


a scientist at a lab bench with samples


With an estimated 50,000 new coronavirus cases per day, and, according to the Office for National Statistics, 618,000 people infected across the UK at the moment,that’s 1 person in every 90,the country is back in a state of lock down. This is despite the UK having one of the highest testing capacities in the world now: over 20 million tests have been carried out - more than double the number in France, Spain, and Italy. But the reason that the coronavirus is so hard to get on top of in many countries is because, in more than half of cases, the infected person has no symptoms. And because we only test and follow up people who have symptoms, we’re missing the majority of the cases. One answer is to just test everybody, and that’s the experiment now going on in the city of Liverpool: mass screening of the entire city to flush out and isolate infectious cases and rein-in the outbreak. So how will it work, what will it prove and what's the evidence from other countries that this might be the right way to go? Chris Smith spoke to epidemiologist at the London School of Hygiene and Tropical Medicine Julian Peto…

Julian - The purpose of mass testing is to identify people before they've infected anybody else, then to lock their household down, and also to trace their contacts rapidly.

Chris - Why have they decided to do this in Liverpool now?

Julian - Because Liverpool's got the highest rate in Britain. So you're testing the approach and addressing an urgent public health problem. The difficulty is, they're launching it within a couple of days of starting lockdown. And of course the infection rate is going to drop very fast anyway, as a result of lockdown, so it's not clear that they'll get very good evidence on how well it's working.

Chris - We know that this has been done. China have famously now done this on the scale of millions, taking cities with 9 million people in them, in some cases, and testing the lot in under a week. So how are they doing it? And if they've proved it works, why aren't we already doing it?

Julian - Well, they weren't doing regular testing. They tested the entire population of the city, that they already had all sorts of stringent sort of testing and tracing, and lockdown processes were going on. The idea that I've been plugging for a long time, is that if you test everybody once a week, you could just end lockdown. You've reduced the rate of transmission so much that we could all go back to the pub, and start going to football matches and kissing our grannies.

Chris - How are they actually going to do this in Liverpool? What's going to be the mechanism for doing these tests?

Julian - People simply volunteer to get tested, I mean some groups such as NHS workers and so on are being targeted, but they've also invited anybody who wants to test to simply go to a testing center and have one. They're using what are called point of care antigen tests, which are tests, which are done on the spot and give you a result within, you know, well under an hour, that's one of the problems with the demonstration projects. I mean, you want to try and test the whole population, not just people who turn up to get tested.

Chris - Slovakia have been doing this as well. Haven't they, in recent days? They have tested at enormous scale, a very large number of people and picked up a significant number of people, who both did have symptoms, but equally those who didn't,

Julian - They tested 3.5 Million out of a population of about 5.5 million over a couple of days. And they're going to repeat it a week later, they found 1% that were infected. It'd be interesting to see what happens when they do it a week later, simply doing it twice every two weeks, I mean like the intervention in Liverpool, which is the same thing, it could knock it down, but of course it won't have any subsequent effect. It'll creep back up again afterwards. You've got to keep it going for three or four weeks, at least, to bring it down to such a low level that you can then do it this frequently. Or we introduce it every month or two, as it starts to creep up again,

Chris - Thinking about the practicalities then of doing this on the scale, not just of a city like Liverpool, but if it's going to be useful, we're going to have to do the whole country. Aren't we? And we're going to have to do it regularly. So in practical terms, can we lay our hands on the sort of testing capacity that we need, and how much is this actually gonna cost?

Julian - As far as the testing capacity goes, by far the cheapest and quickest way of getting the capacity you need, which has in turn been a test today, is a method called lab testing. It's a simplified version of the PCR testing that they're using already.

Chris - And how long would we have to keep doing this for?

Julian - I don't think you need to do it for more than three or four weeks. You might have to do it again a few months later. You wouldn't just go on doing it. I mean, once you got the infection down, to one in several thousand, you'd obviously slacken off and then preferably introduce it later. But it's much nicer to reintroduce mass testing every few months, without any lockdown, so to introduce lockdown it would be a few months.

Chris - So the strategy therefore would be, you take in the entire country, you test everybody, you pick up en masse, all at once, all of the infected cases, whether symptomatic or not, and you isolate them. And because you're doing that all at once en masse, you are breaking the transmission chain, there and then, and that will translate, you're saying, into a big reduction in cases, which buys us a big window effectively, of low levels of virus and, we're effectively almost back to normal, at least for awhile.

Julian - Yeah. So I mean, it's a permanent strategy for keeping going without destroying the economy, until a vaccine becomes available. For a vaccine to be available for the entire population is going to take a long time. I'd be very surprised if everybody's going to get vaccinated within less than a year.

Chris - It sounds like a really compelling case. So why have the government, not just of this country, but many countries not pursued this more aggressively.

Julian - There are a whole series of reasons. I mean, first of all, it's never been tried in any country ever, testing the whole population once a week, to control a pandemic like this. Secondly, there are very strong vested interests involved. I mean, the government's advocating very large contracts for testing and tracing. The method that I'm recommending would be one without their involvement, one rather irritating thing is, that the expert modelers who've been advising the government, didn't think of it themselves and so they reacted by saying: "What an idea!?" Although, there's never been any serious scientific objection raised.


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