 Since the Delta variant arrived in the UK, COVID cases had been spiraling out of control. I say had, because there seems to have been an about face over the past six days. According to NHS data, starting from last Sunday, the exponential rise in COVID cases went into reverse. And for the first time since February, we have seen six consecutive days of declining cases. In the last 24 hours, 24,950 cases were reported, a figure which is down from 40,000 on the same day last week. It's also less than half the daily cases registered just nine days ago, when 55,000 cases were recorded in 24 hours. So what explains this dramatic about turn? Earlier today, I spoke to Billy Quilty, a researcher and disease modeler at the London School of Hygiene and Tropical Medicine. I asked Billy whether we can be confident this decline in registered cases reflects a decline in actual cases and not just less people getting tested. Like the dropping cases over the past week is genuine. Testing is currently has slowed slowly, but it's quite flat. It hasn't dropped to the same extent that we've seen cases drop as. So I think what we're seeing at the moment is changes in behaviour over the short term. So we've basically seen over the past few weeks, the end of the euros and during the euros, there was a spike in young people, most notably in young men, and we're seeing a drop in that age group as the euros have finished. And we also saw this in Scotland when they were knocked out of the tournament. We've also heard a spell of good weather. So there was a heat wave last week and that's going to basically push people outdoors. So their interactions are going to be safer as transmission is less likely to occur outdoors. And we've also had the so-called pandemic. So there was close to half a million people asked to self-isolate in the past week and that is going to have some effect. We've also got at-home testing now. So we may be catching cases and quarantining people earlier than we were before and preventing more transmission that way. Lots of people are quite excited that this seems to be the first time that we've seen cases significantly fall without something like a lockdown. That's got people talking about herd immunity. Do you think this is a sensible moment to suggest that maybe we have reached some kind of herd immunity threshold? I think it's too soon to say that now. I think we've seen cases fall in other countries and that's, for example, India. And that's probably more a result of regional heterogeneity in cases. So we see cases rise and fall in different parts of the country. And that heterogeneity can also be expressed in different groups of people. So during the euros we may have seen more sociable young people form bubbles which then become infected quite rapidly. And we may see that now a large proportion of people in those sociable bubbles have been affected and then we may be seeing the cases drop as we see those bubbles reach herd immunity. But that doesn't apply to the whole country even though we may see cases rise and fall as they move into different bubbles which have less population immunity over the course of the summer. Last Monday was the so-called freedom day. How long will it be until we know how significant effect that will have on case numbers? Could it be that we had a Euro 2020 spike and we're about to see an even bigger freedom day spike? Potentially, although at the same time we've seen schools go out. So lots of cases now because we vaccinated older people and are concentrated in the young. So there's going to be two competing factors there. One that people are having more contacts because of step four but also that children are having less contacts because they're out of school. So it's very uncertain where it's going to go in the next few weeks. One thing that's been notable about this dip in cases is it doesn't seem like anyone saw it coming. We had Neil Ferguson on Andrew Marr just over a week ago saying that it was certain that we were going to go to 100,000 cases a day and then potentially up to 200,000 cases. So why was this not foreseen? And will this change those projections that people have been making over the coming or for the coming weeks and months? So it's pretty difficult to incorporate the kind of behavioural changes we've seen over the past few weeks into large-scale epidemiological models because we can't predict the weather more than two weeks out. So when we have a heat wave, it's very hard to know what effect that will have and what magnitude that effect will have. Well, some models do try and account for behaviour. So the LSHDM model incorporates Google mobility data, but that's only in the past. We don't know how that's going to influence or change in the future and that's on the macro scale. So it's hard to really know that heterogeneity aspect that I was speaking about previously. It's hard to model that on a national scale. So it is worth noting that the roadmap models did have a large degree of uncertainty. So in a way, we are still capturing this effect. So it's still likely within the confidence intervals we've seen. And it's just very hard to know what's going to happen over the next few months. That was Billy Quilty from the London School of Hygiene and Tropical Medicine. Ash, we finally have some good news on COVID. Are you feeling positive about this drop, or are you feeling like you don't get too excited? It's about to get a lot worse and we'll... I mean, look how ridiculous we were to think it was going down. I'd been saying for ages, get the kids out of school, send them home and open the night clubs because you can do your reading, writing, arithmetic at home. But can I dance on a table to got to be real alone in my house? I cannot. So I think that we've always been suffering from this kind of misallocation of priorities. I think one of the things that Billy said, which is really wise, is that there was always a lot of uncertainty in the roadmap and there's never going to be simply one thing which has one set of effects. So obviously more contact because of people being in night clubs will increase a certain amount of transmission. Kids being out of school will reduce a certain amount of transmission. You've got the vaccine in play as well. And also just because you've got night clubs opening doesn't mean you've got all young people behaving exactly the same way. So where there will be a significant portion of people who are like, you know what, like the rules mean that I can get back in the club. I can go to parties. I can socialize indoors. There will still be a chunk of people who feel uncomfortable with doing that or will modulate and adjust their behaviors in all sorts of different ways. And so I think that we can be cautiously welcoming of this good news. I think that we should bear in mind that it's going to be another two, three weeks before we really see the impact of having moved to step four of the unlocking roadmap. But you know what, there's no one, nobody gains by being a deemster and a gloomster to quote Boris Johnson. None of us want to be in a pandemic forever. And if what we're seeing is that the vaccine is having a significant enough of an effect on transmissions that we can reopen and reduce case numbers at the same time, then that's fantastic. But I just think we should be a bit cautious and keep a BDI on the data before we announce mission accomplished on an aircraft carrier. Yeah, I think announcing mission accomplished would definitely be a big mistake at this point. I mean, what is positive from this is if we see cases falling, that means that for a period of time, R was below one. And we can assume that for the past week or so, R has been below one. And to me, what that means is with the current level of immunity we've got, which isn't going to be enough to keep R below one in all situations, that was enough to keep R below one when we happened to have a heat wave. And we didn't really have many mass events. Obviously, most of the clubbing that's taken place after Freedom Day won't yet have fed in. We haven't seen the results from the first actual weekend where people were allowed to go to clubs. But for that period of time where we had very hot weather and no mass events, that was enough to keep R below one and the epidemic shrunk. What we're going to find out in the next week is whether or not we have enough immunity, which is slightly more now than we had a couple of weeks ago, if we have enough immunity to keep R below one when nightclubs are open and when the weather's shit.