zico wrote:Mike4 wrote:A further thought I forgot to include in my first post in this thread, is R0 has conveniently been forgotten by govt, the media and virtually all commentators. Dr John Campbell mentioned it briefly a week or two ago pointing out the Alpha variant is 40% more infectious than the original virus, and the Delta is 60% more infectious than Alpha. Now the original had a natural R0 of approx 3 so that means R0 for Delta must be 3 x 1.4 x 1.6 = 6.72.
Given we struggled to keep the original virus with R0 of 3 under control with our version of lockdown, I can see why the govt has not even bothered to try controlling Delta with it's R0 of 6.72, and elected to follow a strategy of letting it do whatever it likes.
AstraZeneca vaccine reduces infection rates by around 50%.
If everyone was vaccinated, that would give R0 = 6.72*.5% = 3.4
Currently, with only 50% of UK population fully vaccinated R0 will be halfway between 3.4 and 6.7 = 5
(I haven't taken account of the proportion of people with just one vaccination, but one jab only reduces infection by 30%, and also infections are being mostly spread amongst children (completely unvaccinated) and young people without vaccinations who are more likely to be spreaders, based on their lifestyles.
Given this, the R0 may be around 4 rather than 5, but it's very unlikely to be much lower - and the crucial point is that it will be spreading more quickly than the original Wuhan virus did when it first arrived on our shores.
Imagine a game where you enter a large room that has 1,000 people in it all with a bright tag attached by a piece of velcro to their back. You are allowed into the room and given 5 seconds to remove a velcro tag and are a winner if you succeed in that 5 seconds. The tag isn't put back on and the same individuals remain in the room.
Another contestant is allowed 5 seconds to play the game, with 999 people having a tag. It is likely you both will have succeeded.
But that's a linear version and it seems most agree Covid doesn't work like that it is "exponential". So for round 2 instead of a single contestant playing there are 2 people searching for those bright velcro tags. Again both will probably succeed and there will be 997 tags remaining and 3 people without.
Now 4 people play round 3, 8 play round 4 etc. It's not hard to imagine there comes a point, perhaps at this round where only 7 of the 8 win, or 15 of the 16 etc. The game is becoming harder to win at for any individual. After a few rounds most contestants aren't able to win. There is a developing "herd immunity" to the grab a tag game.
Now maybe the rules change and instead of having 5 seconds to grab the tag, you get 10. This new version of the game is more infectious than the first version. The number of rounds before the game becomes harder alters, and so does the number of rounds taken and contestants playing to get 50% of the tags, or 90% or 99%. It doesn't alter the fact that the game gets harder the more rounds you progress.
Nor is it intuitively obvious whether it is easier in round 1 of version 1 of the game, or round 3 (or 4 or 10) of the second version of the game.
In focussing solely on Ro, of either version of the game, and ignoring the number of rounds played, and the diminishing number of tags and only comparing the number of seconds between 5 and 10 allowed in those 2 versions of the game misses a whole lot of what is important, which is how many tags have been taken, and how many are left.
Now imagine a version of the game, developed in Oxford, where at the end of each round 100 of the people in the room are removed from the game to "safety". That makes it harder still to find a "tag" to grab. If the numbers being removed is sufficiently large, the effect of removal is greater than the increase from 5 to 10 seconds.
No doubt there could be many modelled versions of the game with attempts to work out a way to ensure the fewest tags are won by contestants. No doubt some would only focus on the number of seconds in the rules, and not the other variables. It wouldn't surprise me if some people thought that in every version of the game all the tags would always be got. A larger number would possibly believe there would be similar outcomes regardless of how the variables would change, and that the original rules should always apply and no variation in strategies in "surviving" playing should be allowed.