Intended for healthcare professionals


Covid-19’s known unknowns

BMJ 2020; 371 doi: (Published 19 October 2020) Cite this as: BMJ 2020;371:m3979

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  1. George Davey Smith, professor in clinical epidemiology1,
  2. Michael Blastland, writer and broadcaster2,
  3. Marcus Munafò, professor of biological psychology1
  1. 1University of Bristol, Bristol, UK
  2. 2Winton Centre for Risk and Evidence Communication, Centre for Mathematical Sciences, University of Cambridge, Cambridge, UK
  1. Correspondence to: G Davey Smith PA-ieudirector{at}

The more certain someone is about covid-19, the less you should trust them

In 2019, the medical historian Mark Honigsbaum concluded his book The Pandemic Century by saying: “The only thing that is certain is that there will be new plagues and new pandemics. It is not a question of if, but when.”1

Look around and you might wonder if he was hopelessly wrong. Not about the pandemic, which turned up almost before his ink was dry, but about there being only one certainty. In the “science” of covid-19, certainties seem to be everywhere. Commentators on every side—academic, practitioner, old media or new—apparently know exactly what’s going on and exactly what to do about it.

We are not talking about those who insist that hydroxychloroquine will save us all, or who call face masks “muzzles” or “face nappies,” or who declare that many detected covid-19 cases are false positives. We can also leave aside those who sidestep reality to suggest that we’ll have a world free of covid-19 within months if we simply follow their advice.

Rather, we are thinking of the many rational people with scientific credentials making assertive public pronouncements on covid-19 who seem to suggest there can be no legitimate grounds for disagreeing with them. If you do, they might imply, it’s probably because you’re funded by dark forces or vested interests, you’re not evidence based, you’re morally blind to the harm you would do, you’re ideologically driven (but I’m objective), you think …

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