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expert reaction to preprint from Imperial College looking at hospitalisation risk for Omicron cases in England

A preprint, an unpublished non-peer reviewed study, from Imperial College London models hospitalisation risk for Omicron cases in England.

This Roundup accompanied an SMC Briefing.


Dr Raghib Ali, Senior Clinical Research Associate, MRC Epidemiology Unit, University of Cambridge, said: (comment also referring to the EAVE II preprint which you can read here: and third party comments here:

“The first UK data from Scotland and England on the severity of Omicron for hospitalisation is encouraging with the risk of admission being about two thirds lower in the smaller Scottish dataset and about half in the larger English data set.

“Although preliminary, both these studies provide reassurance that infection with Omicron is less likely to result in hospital admission than with Delta.

“This is the key data point we needed to estimate the likely peak and total number of admissions in the coming weeks. And while further data is needed to confirm these studies, the worst-case scenarios that were presented last week can safely be excluded.”


Prof James Naismith, Director of the Rosalind Franklin Institute, and Professor of Structural Biology, University of Oxford, said:

“This second study is less positive than the EAVE II study, that they report different outcomes is part of science. Both studies are early and we should expect different results as the science evolves.

“This study finds that previous infection reduces the risk of hospitalisation by around two thirds, indicating Omicron is milder if you have some immunity.

“However, the study suggests there is no reduction in the severity of Omicron compared to Delta for the doubly vaccinated, indicating that it is not milder.

“This finding is surprising but is grounded in data. There is no report on the benefit of boosting.

“The study highlights the same risk as EAVE II, Omicron is not a harmless  infection, it will cause serious illness and the more people it infects the more people will end up in hospital.

“Decreasing the spread of the virus to give time to improve population coverage with the booster is the best strategy.”


Prof Penny Ward, Independent Pharmaceutical Physician, and Visiting Professor in Pharmaceutical Medicine at King’s College London, said: (comment also referring to the EAVE II preprint which you can read here: and third party comments here:

“On a day when the UK has registered its largest ever number of daily confirmed COVID infections, some good news has emerged from Scotland and from Imperial College. Both studies suggest that infection by the omicron variant may be less severe than infection by the delta variant, when assessed by comparing the proportion of patients needing hospital admission. At this point, both studies are based on comparisons with differing follow up periods due to the more recent appearance of the omicron variant, leaving some degree of uncertainty as to the potential for more severe outcomes among subjects affected by the omicron variant that do need hospital admission to emerge later. However, based on this preliminary information, the decision to delay imposition of greater restrictions on social mixing than are currently advised under Plan B might be more reasonable than some have suggested. This news does not detract from the extraordinary spread of this variant across the population, and the fact that even a small proportion of people needing hospital care for COVID may become a very large number indeed if the community attack rate continues to escalate, with all that implies for overstretching the already stretched NHS. It remains important for all of us to take reasonable care, test test test, and get our boosters as soon as possible. If we all do this, then we might expect a happier new year 2022 than at the same time last year.”



‘Report 50 – Hospitalisation risk for Omicron cases in England’ by Neil Ferguson et al. is an unpublished preprint



All our previous output on this subject can be seen at this weblink:



Declared interests

None received.

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