The herd immunity article helpfully provides a timely overview of the various, hard to quantify factors that interact with each other when it comes to herd immunity. But as I mentioned before, I'm still somewhat puzzled by how the recent sharp rise of infections in the UK (as well as places like Spain and the Netherlands) happened. I thought the vaccination progress plus immunity acquired from prior infection would slow such a rise. But maybe a large event as the football Euros really worked as a catalyst.