Michael Simmons Michael Simmons

Sage scenarios vs actual: an update

Modelling from the London School of Hygiene & Tropical Medicine showing Covid beds occupied (19 December)

‘Deaths could hit 6,000 a day,’ reported the newspapers on 17 December. A day later documents for the 99th meeting of Sage were released which said that, without restrictions over and above ‘Plan B’, deaths would range from 600 to 6,000 a day. A summary of Sage advice, prepared for the Cabinet, gave three models of what could happen next:

  • Do nothing (ie, stick with ‘Plan B’) and face “a minimum peak” of 3,000 hospitalisations a day and 600 to 6,000 deaths a day
  • Implement ‘Stage 2’ restrictions (household bubbles, etc) and cut daily deaths to a lower range: 500 to 3,000.
  • Implement ‘Stage 1’ restrictions (stay-at-home mandates) and cut deaths even further: to a range of 200 to 2,000 a day

After a long and fractious cabinet debate, the decision was to do nothing and wait for more data. ‘Government ignores scientists’ advice,’ fumed the BMJ. But the decision not to act meant that the quality of Sage advice can now be tested, its ‘scenarios’ compared to actual. 

Sage/Warwick hospitalisations

Let’s start with the Warwick model. It published various Covid scenarios depending on Omicron’s possible ‘severity’: 100 per cent as severe as Delta, 50 per cent, 20 per cent and 10 per cent. A UK Health Security Agency (UKHSA) document released on New Year’s Eve said: ‘the risk of presentation to emergency care or hospital admission with Omicron was approximately half of that for Delta’.  That’s still its best estimate. So we open with the 50 per cent severity scenario. Here’s how Warwick’s model is performing for hospital admissions:



So: pretty far out. The Warwick scenario which closest matches actual hospitalisations in England is the one that assumes Omicron is 10 per cent as severe as Delta. But no one has ever claimed the new variant is as mild as that. 

Hospital occupancy: the Sage/LSHTM model

The justification for restrictions is to prevent Covid from overwhelming the NHS, so hospital capacity is perhaps the single most important Covid figure. The 101st Sage meeting on 19 December included another statement



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