The BBC website indicates that there were quite a number of Covid -19 deaths in the Leicester area (particularly in South-West Leicester) in May, so this is not just a recent problem.
If Herd Immunity was not working, we would be seeing flare-ups in all the areas where there were BLM demonstrations.
There is no coast in Leicester - and no tourist attraction that I know about.
Places like London, which had a large number of cases early in the pandemic, now seem to have herd immunity - perhaps Leicester is just catching up?