We don’t currently have any countries with a large number of cases where the doubling time is >6 days and holds steady for a prolonged period.
I spent a few days looking at this, doing simulations etc. The zone where you slow the growth rate to a low rate, not exploding and not collapsing, is very narrow. It is roughly R0 = 0.98 to 1.10.
So, given
1. The effect on R0 of a given set of measures is quite uncertain and hard to predict, and
2. To flatten the curve without causing a collapse in cases you need to hit a very narrow zone,
the implication is that to be confident that you will not have an explosion, you need to target an implosion in cases. If you think you can finesse “how much can we get away with” you are probably kidding yourself.
Yes, holding at a high number is tricky and not particularly desirable. If you get doubling time above 6 days then it’s likely that you’ll start decreasing cases.
I think that the most important thing if trying to hold at a low level whilst relaxing restrictions is ensuring that the doubling time is longer than the incubation time (which is the main lag in your control loop). That way if you have made an error the virus isn’t too far gone before you start to notice and contact tracing for containment remains viable.
This seems to suggest we will experience a cyclical pattern to these events. When we transition to a R0 < that .98 we seem to have things under control and will likely start seeing either relaxing any imposed controls or just relaxing our self imposed constraints on interactions. Then we’ll have a few new infections, and R0 then returns to a value above the range so we’re back in the epidemic spread phase again.
I also notice a lot of countries have had two peaks. Possibly this is a combination of stopping overseas visitors, combined with testing focused on overseas arrivals (and neglecting local transmission which is harder to find), combined with a ramp-up of testing which produces a spike in apparent cases.
Do the initial lull in confirmed cases is likely to be a false dawn.
Thank you—this is very helpful to me.
I spent a few days looking at this, doing simulations etc. The zone where you slow the growth rate to a low rate, not exploding and not collapsing, is very narrow. It is roughly R0 = 0.98 to 1.10.
So, given
1. The effect on R0 of a given set of measures is quite uncertain and hard to predict, and
2. To flatten the curve without causing a collapse in cases you need to hit a very narrow zone,
the implication is that to be confident that you will not have an explosion, you need to target an implosion in cases. If you think you can finesse “how much can we get away with” you are probably kidding yourself.
Yes, holding at a high number is tricky and not particularly desirable. If you get doubling time above 6 days then it’s likely that you’ll start decreasing cases.
I think that the most important thing if trying to hold at a low level whilst relaxing restrictions is ensuring that the doubling time is longer than the incubation time (which is the main lag in your control loop). That way if you have made an error the virus isn’t too far gone before you start to notice and contact tracing for containment remains viable.
This seems to suggest we will experience a cyclical pattern to these events. When we transition to a R0 < that .98 we seem to have things under control and will likely start seeing either relaxing any imposed controls or just relaxing our self imposed constraints on interactions. Then we’ll have a few new infections, and R0 then returns to a value above the range so we’re back in the epidemic spread phase again.
Does that seem right from this?
I also notice a lot of countries have had two peaks. Possibly this is a combination of stopping overseas visitors, combined with testing focused on overseas arrivals (and neglecting local transmission which is harder to find), combined with a ramp-up of testing which produces a spike in apparent cases.
Do the initial lull in confirmed cases is likely to be a false dawn.