Thought I'd share this graph from PH England's '
Weekly National Influenza and COVID-19 Surveillance Report'
The lines shows results of blood analysis (extrapolated and weighted (by age group, sex and NHS region)) for Roche (S) test (black line) showing both vaccine-induced and previous infection induced C19 antibodies; and Roche (N) test (red line) showing just previous C19 infection induced antibodies.
The dataset is up to about 6 days ago and is over 18s in England. The final datapoint on the black line aligns pretty well with the percentage vaccinated by 10 March (14 days before, to allow the vaccine to 'work').
Given:
1) There is a significant seropositive element in the population, without having been vaccinated: 15% (red line above - it averages a little higher in the 18-49s btw); About 22M adults have not been vaccinated: of those 15% who have antibodies is therefore 3+M.
2) 59% of the adult (O/18) population have received their first dose (31M).
3) 75% of the total UK population (ie including the 14M under 18s) is 50M.
Caveats:
# If the vaccination programme proceeds as planned (assumes a resumption of better supply from late April onwards) and
# if herd immunity is achieved at 75% vaccination (see previous posts on discussion of the factors: vaccine % effect on transmission as opposed to 'just' prevention of symptomatic illness, NPI (restriction) measures limiting 'R', dominant variant no more infectious than current)
Then my estimate is that we might reach 'herd immunity' by 14 July. The impact we'd see is that the daily case figure which is likely to rise in the next 6 weeks (NB but not result in severe illness increase - this will decline - cases and hospitalisations have been disconnected by vaccination of the vulnerable half of the population) will tail away in late June onwards and the test and trace mechanism can concentrate on what it can probably manage: whack-a-mole (both outbreaks and VoC discoveries).