If the new strain is more infectious..15 Dec 2020 08:47
Slowly sinking in why they would look so worried if the new strain is more infectious..
Firstly, the government are aiming to keep cases below the level hospitals can cope with by keeping R0 below 1.
For covid, estimates of R0 are between 2.5 and 3.5.
The levels of lockdown we have are just about keeping R0 around 1 and leaving the economy barely limping along.
To do the same thing for a more infectious virus with higher R0 (measles has R0 of 12-18) could mean much more demanding lockdowns to keep within the limits of the health service. Implications for the economy could be massive and another question is whether the UK population would do what is needed without riots or just ignoring the rules.
Secondly, there is a vaccination program with the aim of achieving herd immunity so we can get on with a more normal life, stop illness and death and get the economy back to life. Ignore for a moment that the concept of herd immunity requires the vaccine to make people immune ie. not able to be infected or pass on the virus, which there is no current evidence the available vaccines will do.
But, Percentage population for herd immunity = 1 - (1/R0).
So, for the current R0 of 2.5-3.5 the figure of around 70% of the population is often cited.
If the virus becomes as infectious as measles, with R0 of 12-18, percentage of population required for herd immunity rises to 92-94%.
This is percentage of population taking a vaccine with 100% efficacy, or 100% of the population if the vaccine has 92-94% efficacy. This would be very hard to achieve in practice.
But this puts into perspective how the AZ vaccine with 62% efficacy from the useful trial data could fall very far short of getting life back to anywhere near normal in terms of social distancing or allowing the economy to get back on track.