Why Vaccination Won’t Stop Everyone from Catching Covid before Long. By David Evans.
Here are the latest official figures on the two vaccines on offer in Australia:
Pfizer reduces your chances of catching covid by about 83%, AZ by about 61%. The official accounts telling us to vaccinate omit the fact that this effectiveness wears off fast, with Israeli data indicating that for Pfizer the effectiveness drops to 16% after 6 months. (This is the data that roiled world markets two weeks ago.)
But the R0 — the average number of people infected by each person with covid — was about 3 for original covid and may be about 8 for delta in unvaccinated people:
With vaccination, the initial R0 of delta drops by 83% to about 1.4 for Pfizer, and about 3 for AZ. It then rises with time, as protection wears off. An R0 of over one means the virus spreads and herd immunity is not achieved.
But vaccination may also reduce the rate at which an infected person spreads covid. One would expect it helps initially, and there are signs of this. But vaccination might increase the probability of spreading in the longer term, because it allows vaccinated people to have higher virus loads for longer (even while they are protected from bad symptoms).
This accords with previous modeling we quoted on the Wentworth Report showing that herd immunity would require 90% of the population to have Pfizer, or 110% of the population to have AZ. That is, we cannot reach herd immunity at all on AZ, and only by 90% coverage with Pfizer.
The picture is not yet clear, but at the moment it looks as though vaccination will not be enough to stop covid from spreading.
It doesn’t appear that Australian policy makers have firmly grasped this yet, or they wouldn’t be talking about opening up and exposing the Australian population to covid soon.
This first generation of vaccines are not the ones we are waiting for.