© Pippa Fowles / No 10 Downing Street
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.
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 data scientist Joel Smalley.)
Immunity to ordinary respiratory viruses occurs mainly through T-cells which 'take a picture of the invader' at a molecular level, 'reproduce' it on certain immune cells and essentially 'never forget a face'.
This T-cell immunity is robust and durable. Those exposed to the highly related SARS virus in 2003 still have this immunity 17 years later. In relation to SARS-CoV-2, the pattern of immunity to date is identical and after around 800 million infections across the world,
there is no convincing evidence for significant levels of re-infection. Not only are those who've been infected and have now recovered immune (they cannot get ill again with the same virus), but importantly
they do not participate in transmission. (See
my article on what SAGE got wrong for
Lockdown Sceptics.) Furthermore, because the immune response is diverse, a proportion of them will also be immune to novel but similar viruses in the future.
Comment: See also: