Please Please update your billing information The subscription details associated with this account need to be updated. Please to continue enjoying your subscription. Your subscription will end shortly Please to continue enjoying your access to the most informative and considered journalism in the UK. The idea of the needs of the collective subsuming those of the individual is antithetical to much of western culture. According to the government’s chief scientific adviser, we might have to reacquaint ourselves with the concept. Because to control coronavirus, says Patrick Vallance, will require something called “herd immunity”. It will also require controlling who in the herd it is who gains that immunity. Sponsored Herd immunity does not require everyone in Britain’s “herd” to be infected. It happens before that, when just a proportion of them have. That proportion is the second most important number in epidemic modelling. To see how it is calculated — and perhaps even changed — requires, however, understanding the most important number Get in touch More from The Times and The Sunday Times © Times Newspapers Limited 2021 . Registered office: 1 London Bridge Street, SE1 9GF.