by Dr Mike Yeadon Chief Medical Officer, Professor Chris Whitty and Chief Scientific Adviser, Sir Patrick Vallance give a Coronavirus Data Briefing in 10 Downing Street on September 21st. Picture by Pippa Fowles / No 10 Downing Street. How a novel virus met a partly-immune population In Spring 2020 a novel coronavirus swept across the world: novel, but related to other viruses. In the UK, unknown at the time, around 50% of the population were already immune. The evidence for this is unequivocal and arose due to prior infection by common cold-causing coronaviruses (of which four are endemic). This prior immunity has been confirmed around the world by top cellular immunologists. There is even a very recent paper from Public Health England on the topic of prior immunity and a wealth of other evidence from studies on memory T-cells, studies on household transmission and on antibodies. Because of the extent of the prior immunity, and as a result of heterogeneity of contacts, once only a low percentage of the population, perhaps as low as 10-20% had been infected, “herd immunity” was established. This is why daily deaths, which were rising exponentially, turned abruptly and began to fall, uninterrupted by street protests, the return to work, the reopening of pubs and crowded beaches during the summer. (See this explainer by the ...