RO value, can anyone explain? Can we eradicate?

[Chosennone]

Sorry if I'm being dim. I am reading around a lot, however, I'm just a bit unsure about the talk of RO value. Sir Patrick Vallance was talking about it at the update yesterday. He says we have managed to reduce it to around one from 2.5. So I get that means the virus isn't spreading as virulently. I thought the message was clear that the movement restrictions/soft lockdown are to save the NHS and flatten the curve etc. I get that reducing the RO means the spread is slowing and we should see a drop off now of new infection.

But is there an idea that the virus can be 'controlled' got back on top of? As in could the go back to the containment phase? Or will we just turn the tap on and off Lockdown wise. I know we are looking at China and then Italy and Spain to see what happens next, but what is the aim here? TIA

My understanding is that the "contain phase" works in the early stages of the spread when virus is isolated to a particular location/cluster of people. For example, China locked down Wuhan to try to contain it in that area. Now the virus has moved through every county in the UK it is no longer able to be contained as it is essentially distributed everywhere. That means once lockdown restrictions are relaxed it will start spreading again but we will have no way to predict where and to whom so contact tracing / quarantine will be near impossible. That's why if you miss the opportunity to contain it then you're never getting that opportunity back.

It's explained very well on the graphs thread.
On our (Italian) lunchtime news they just said in Spain it was down to 0.7 which is why they are relaxing the more stringent measures.

RO 2.5, one person infects on average 2.5 people.
10 people therefore infect 25 people. Thus the virus keeps spreading.
RO 1, one person infects on average 1 person.
10 people therefore infect 10 people, some won't infect any some will infect 2 or more people. So the virus keeps spreading but at a lower rate.
RO 0.5, one person infects on average half of a person.
10 people therefore infect 5 people. Still some could infect more than one person but more affect none. So the rate of spread drops.

I don't know what RO would be needed to eradicate it completely, RO of 0 I suppose. Not sure that's possible to get, maybe an RO of 0.005 would be considered acceptable.

Anyone know what RO would be needed to release the current lockdown?

That's why if you miss the opportunity to contain it then you're never getting that opportunity back.

Unless you reduce to manageable numbers again.

The RO value is a result of how infectious the disease is, the level of immunity in the community and the strength of social distancing measures. If we let the virus run its course then eventually we would get to RO nearing zero because it would spread like wildfire and the population (who didn't die) would become immune. This would be a sensible strategy if the virus wasn't so deadly but obviously we can't countenance that many deaths. So we have artificially lowered our RO number by enforcing a lockdown. As soon as it is lifted the RO number will rise again as OP said.

I don't know what RO would be needed to eradicate it completely, RO of 0 I suppose. Not sure that's possible to get, maybe an RO of 0.005 would be considered acceptable.

An R0 or less than 1 will cause it to die out. A R0 of 0.005 would cause it to die out very fast indeed!
1,000,000 infect people would only infect 5,000, who in turn would infect 25, who by the law of averages wouldn’t infect anyone new. If the infection period was 5 days, there would be no more new infections after 10 days or so!

In theory, an R0 below one will eventually result in the disease dwindling away to nothing, it’s just a matter of how long it takes. But the cost of doing that has to be weighed up against other considerations, i.e. the health, social and economic cost of lockdown

In theory, an R0 below one will eventually result in the disease dwindling away to nothing, it’s just a matter of how long it takes

The point is though that the RO has been artificially generated through the lockdown measures. So as soon as those are relaxed it will jump back up again. That is unless we find a way to contact trace and quarantine everyone who has it which seems almost impossible given that so many people can be asymptomatic.

But the only reasons that contact tracing has failed in the countries that have been suscessful ( despite asymptomatic people) was that they forgot to isolate people who had contact with new arrivals who were quarantined.

So whilst it's not easy and you are always trying to stay a step or two ahead, it does seem like it's possible

The graphs thread makes for very interesting reading. Some very knowledgeable people on there.

I wonder if it could get that low that the virus peters out or 'runs its course'. Is that scientifically possible?, if it started with one bat/pangolian and one human it clearly has run amok. If it got down to just a handful of people it would all start again wouldn't it? I guess the immunity is going to be a key issue here.

Unless you reduce to manageable numbers again

It's not about numbers it's about knowing where it is. You can only contain the virus if you know where it is. But now it is everywhere and we will never practically be able to do testing at the scale that's needed to find out who has it / has had it. It only takes one person to start spreading the virus without us knowing and we've got a pandemic again. I don't want to sound all doom and gloom but logically I just don't see a way out.

If it got down to just a handful of people it would all start again wouldn't it?

Yes exactly. If you knew who those handful were then you could contain it. But if you don't then yes you are buggered.

I wonder if it could get that low that the virus peters out or 'runs its course'. Is that scientifically possible?

It is - but both getting to that point and then maintaining it isn't easy. There are several countries that, so far, appear to be having some success - China, New Zealand, Norway. Time will tell how viable this is an approach, but it's got to be a better plan A than herd immunity!

Yes, even one person can lead to a resurgence

Which is why a test and trace with on going although less stringent distancing is probably the only way to go

If you find a person and track back everyone they contacted and forward trace everyone they contacted you can control it

Not perfect but you should be able to keep deaths in the tens rather than tens of thousands , where the risk is then comparable to say going for a drive