Intended for healthcare professionals

Letters Covid-19: shielding versus blanket policies

Our choice is not binary between lockdown and herd immunity

BMJ 2020; 371 doi: (Published 22 October 2020) Cite this as: BMJ 2020;371:m4051
  1. K K Cheng, director
  1. Institute of Applied Health Research, University of Birmingham, Birmingham B15 2TT, UK
  1. k.k.cheng{at}

All scientists who argue for caution share Sikora and colleagues’ desire for normality.12 Our case against their position has been made in the letter by Greenhalgh and colleagues,3 of which I am a signatory. On the risks of attempting herd immunity, even if we optimistically assume that immunity would persist after infection and that vulnerable people can really be shielded, infecting, say, half of the 35 million younger people (20-59 years old) in the UK has serious consequences despite the lower risk of serious acute complications. Conservatively, in this age group there would be at least 10 000 deaths, 50 000 hospital admissions, and hundreds of thousands of people with long covid.

Some people argue that we could reach herd protection by infecting fewer than 50% of younger people, but there are no supportive data for the potential reasons they put forward. On the other hand, in Manaus, Brazil, the prevalence of covid-19 seropositivity among blood donors reached 66% in June,4 which for several weeks gave the local population hope that herd immunity had been reached as incidence seemed to slow down. But the incidence is rising again.5

The Great Barrington Declaration approach will not work. No countries have shown that they can shield vulnerable people when community transmission becomes widespread, for the obvious reasons that people at high risk are cared for by young health and social care workers or family members. But our choice is not binary between lockdown and herd immunity. We have a fighting chance of keeping most things open without national lockdown this winter if we have an improved find-test-trace-isolate-support system, sensible social distancing, high usage of masks, good border control, and clear communications that engender public trust. All these things are feasible in well governed, high income countries.


This article is made freely available for use in accordance with BMJ's website terms and conditions for the duration of the covid-19 pandemic or until otherwise determined by BMJ. You may use, download and print the article for any lawful, non-commercial purpose (including text and data mining) provided that all copyright notices and trade marks are retained.


View Abstract