And this is why I’m suggesting that recently acquired immunity in the 18-29 age group could possibly be important in explaining the recent downward trends.
Yes, I agree.
Interestingly, if we had achieved a natural HIT threshold we could have expected a very slow decline, not a sudden drop.
I am wondering if we had been close to the HIT threshold in some areas in early July with Bolton and Blackburn potentially leading the way. Both places might have peaked naturally and started the expected slow decline (with occasional ebbs and flows). However, a series of super spreading events (Euro 2020 matches) pushed R up massively across whole of England and led to "front loading" of infections in susceptible population (younger age groups who have not yet been fully vaccinated).
When Euro finished, R went back down and by then the pool of susceptible population has been significantly depleted. The expected slow decline turned into the fast drop.
I don't know if it makes sense but this is my current hypothesis.