Here in the UK we're heading towards deep trouble in just 11 days time when the UK relaxes most covid rules; the so-called "freedom" day. 😟
The delta variant is around 55% more transmissible than the alpha variant. The Alpha variant, in turn, is about 50% more transmissible than the original Wuhan virus.
The R figure for the original Wuhan virus was around 3. That is to say, given we freely intermingle and no one is immune to the virus, then each infected person will, on average, infect 3 others.
Assuming that figure of 3 was roughly correct, then the alpha variant R figure is 50% higher than this figure of 3, or 1.5 times 3 = 4.5. The delta variant is 55% more transmissible than the alpha variant. That's 4.5 + (0.55 times 4.5) = 6.975. Let's just call it 7. The R rate for flu is only 1.3. 7 compared to 1.3!
So, in a world where just one person has the delta variant and no-one is yet immune, the number of infected will very rapidly increase:
1
7
49
343
2,401
16,807
117,679
823,543
5,764,801 etc
In order to avoid exponential growth of the number of infected the R figure has to drop below 1. R is 7 given no-one is immune. In order for that to dip below 1 then over 6 out of 7 people, or 86% of the population, will have to be immune. Note that this is the entire population, not just adults.
In the UK about 85% of adults have been vaccinated. But that's adults only. Around 21% of the population are below 18 years of age, and hence 79% are adults. So that's 85% of 79%, in other words 67% of the entire population.
So 67% of the population have been vaccinated and 86% of the population have to be immune for R to dip below 1. Moreover, vaccines are far from perfect. So we can conclude that the virus will continue to spread despite so many people having been vaccinated. To prevent this, not only should freedom day be cancelled, but since the current R rate is estimated to be about 1.3 to 1.4, the current rules need to be tightened.
Relaxing most covid rules, and especially relaxing the rules about face masks is, quite frankly, reckless and foolish. Not just for the UK, but for the whole world. It's going to allow the virus to spread even more rapidly than it already is. And it's not just deaths we should be concerned about. There's also long covid. But, most concerning and of crucial importance, is the possibility of new variants being created that our vaccines are less effective against.
Update 24/07/2021 Just read the following Guardian article. It says:
The threshold for herd immunity with the Delta variant is unclear, but scientists estimate that transmission would need to be blocked in about 85% of the population.
That's the same as my calculation above. I concluded roughly 86% of the entire population need to be immune.