What SAGE got wrong

On March 16 Boris Johnson held his daily COVID briefing and for the first time introducing tentative social distancing measures. That same day Neil Ferguson had formally  published his simulation of how the UK epidemic would unfold and which suppression measures were needed – Household Quarantine, Place Closure, Case Isolation and Social Distancing (Report 9).  The paper must have been circulated within SAGE far earlier than that.  A full lockdown was finally introduced a week later on March 23. Unfortunately Fergusson’s  timing was about a  month out of date and the real situation was far worse than even he assumed. The real number of cases and rate of infection by March 16 in the UK was in reality far higher. However  no-one knew this at the time because there was no community wide testing amid what now appears to be an air of complacency by PHE.

We can now look back and compare what actually occurred with the original Report 9 simulations which I have rerun. This is shown in Figure 1.

Figure 1. Neil Ferguson’s COVID simulation results (Report 9) as compared to actual COVID deaths as recorded in English Hospitals. The peak in English deaths occurred on April 10. This is compared to the Report9 green lockdown simulations and  a one month delay (solid black) of the model.

The peak in infections and deaths occurred one month earlier than he or anyone else had anticipated. Fergusson had predicted in report 9 that the peak would occur much later  around mid May. That was probably because he was using the Chinese data for R0 (2.4) and used an optimistic estimate of  the number of current UK infections. When the report was published there had been very few confirmed deaths.  However we now know there were probably  tens of thousands of infections. SAGE  now estimate that R0 in early March was 3 and that the number of infections was doubling every 3 days.

If the UK had locked down a week earlier the resultant number of deaths would have been much lower with at least 20,000 fewer deaths and we would be exiting lockdown by now (June 7). However at the time no-one knew the full extent of infection due to the total lack of community testing.

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14 Responses to What SAGE got wrong

  1. Andrew Carey says:

    The first graph is the only one you need to read.
    If the UK had abolished the NPPF and made hand washing compulsory at airports and international train stations, then we wouldn’t have needed to lock down at all.

  2. Hugo says:

    As it now shows in statistics like in the Netherlands, lockdowns at home and in care homes made things way worse. Same for hospital IC.s.
    The spreading is mostly with in same groups and in confined bad ventilated spaces.
    So the Chinese model was flawed from the beginning they made it way worse.
    Its not water drops which spread but much finer aerosols. Breathing. Viral load in combination with age and initial health is what makes it deadly or not. That’s why so many doctors also got infected and died in Italy.

    • Hugo, can you tell us why the statistics in Netherlands show that?

      And how do you know that CoV2 is spread mainly in fine aerosols?

      I’ve seen evidence that talking spreads it – worse shouting or singing.

  3. J Martin says:

    One week earlier, according to Ferguson’s model. Accordng to CEBM Oxford, infections peaked a week earlier than lockdown, so 16th of March, so intervention would have needed to have been substantially earlier than that. Early March or more likely, late February.

    • Clive Best says:

      An interesting theory is that only about 20% of the population are susceptible and the rest of the population are “dark matter” to the virus. So to reach “herd immunity” with an IFR = 0.5% would lead to 47000 deaths. If that were really true then we could go back to normal soon. I have my doubts though.

  4. MarkR says:

    Can you find any details behind those headline UK antibody test numbers? 17% inside London and 5% outside, I couldn’t find the exact dates, sampling strategy & size or test accuracy.

    • Clive Best says:

      I think the definitive result is from ONS. This is a bit out of date but

      As of 24 May 2020, 6.78% (95% confidence interval: 5.21% to 8.64%) of individuals from whom blood samples were taken tested positive for antibodies to the coronavirus (COVID-19). This is based on blood test results from 885 individuals since the start of the study on 26 April 2020.

      I think that London is more like 17-18%

      • MarkR says:

        Thanks Clive, for some reason I couldn’t find that.

        Too little information to directly provide an IFR constraint without some assumptions I’d hoped to avoid. Still hoping the lower values (UK wide 0.5%) are more likely than the higher ones.

  5. None of this is obvious to me.

    I appreciate that you’re treating Covid as a black box, and running some simple maths to see how the result matches observations.

    But we have to model both infection rates and lethality, when we only have deaths as a reliable dataset.

    (And how reliable are deaths for making international comparisons? Probably not very.)

    If the virus becomes slightly milder during the epidemic, the lethality changes and although the pattern may match a certain set of parameters in models, the resemblance may be superficial.

    Covid seems to be becoming milder – but we don’t yet know for certain how much milder.

    What I’m convinced of is that there are MANY strains, all with slightly different properties and pathogenicity.

    FWIW latest, improved version of my video looking at seasonality/selective trends is here:


  6. BBC Radio 4 series “More or Less” is always a good listen (https://www.bbc.co.uk/programmes/b006qshd), and today’s episode particularly relevant:

  7. Michael Rodwell says:

    Prof Ferguson report 9 specifically excluded lockdown. How can he now recommend it should have occurred earlier?

  8. Listening to Rory Stewart interview reminded me that at the time SAGE was convinced that there would be a lethal rebound as soon as lockdown was released.

    This doesn’t seem to be the case. In fact – in spite of what most academics are stubbornly insisting – there are multiple strains and the milder ones seem to have been selected. So the disease is becoming milder – probably.

    Therefore locking down early while the virus evolved was the right thing to do.

    The economic cost of one extra week of lockdown at the beginning was trivial. The epidemiological benefits would have been huge.

    But it was that crucial mistake of understanding by SAGE and others that drove the incorrect decision.

    Very strange then that many academics still insist that there has only ever been one strain and that the disease has not changed. If that were true the decision (not to lockdown quickly) would not have been wrong. They are having cake and eating it.


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