“What we have got now is a really fine balance between something that looks like a lower risk of hospitalisation – which is great news – but equally a highly transmissible variant and one that we know evades some of our immune defences, so it is a very balanced position,” Jenny Harris, chief executive of UKHSA, told the Today programme on BBC Radio 4. However, modelling suggests that the severity of omicron would need to be around 90 per cent lower to avoid similar levels of hospital admissions to previous waves, according to minutes from a meeting of the UK government’s Scientific Advisory Group for Emergencies on Monday. The difference is somewhat larger than suggested by a study published by Imperial College London on Wednesday, which reported a 15 to 20 per cent lower risk.

This is based on a preliminary analysis of 114,144 omicron cases and 461,772 delta cases occurring between 22 November and 19 December. The UKHSA report also estimates that someone infected with omicron is 50 to 70 per cent less likely to be admitted to hospital, compared with delta. For those who had two initial doses of Pfizer/BioNTech, protection falls from 70 per cent at 2 to 4 weeks to 45 per cent at 10 weeks after a Pfizer booster, but stays around 70 to 75 per cent up to 9 weeks after a Moderna booster. For people who had two initial doses of the Oxford/AstraZeneca vaccine, the UKHSA estimates that Pfizer/BioNTech or Moderna boosters are around 60 per cent effective at preventing symptomatic infections from omicron 2 to 4 weeks after the third dose, but this falls to 35 to 45 per cent by 10 weeks.

Based on an analysis of 147,597 delta and 68,489 omicron cases, the agency found that the Oxford/AstraZeneca, Pfizer/BioNTech and Moderna vaccines are less effective against omicron than delta.

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