At the beginning of the year, as vaccine rollouts were starting to accelerate, there was widespread optimism about the outlook for 2021. A mainstream view was that vaccinating a large majority of adults would be enough to reach ‘herd immunity’, the point at which the virus would struggle to spread as it ran out of susceptible hosts. As summer heads into autumn in the northern hemisphere, that point remains elusive. The combination of a more transmissible variant (Delta), and the…