Small population studies in England and Scotland suggest a reduced risk of hospitalisation from the Omicron variant of between 40 and 68%

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Two preliminary studies in the UK have suggested that the Omicron variant of SARS-CoV-2 may lead to lower rates of hospitalisation than the Delta variant.

A comparison of the effect of both variants in England and Scotland give an early indication that Omicron could lead to less severe outcomes than Delta.

Publication of the papers, neither of which have yet been peer-reviewed, came as the UK Health Security Agency prepared to release its own weekly analysis of COVID-19 infections.

An investigation by the University of Edinburgh suggests that Omicron is associated with a two-thirds reduction in the risk of being hospitalised with COVID-19 compared with Delta. 

Meanwhile, research by Imperial College London estimates a 40–45% reduction in the risk of hospitalisation with Omicron for at least one day compared with Delta.

Findings from both preprints have been shared with the Scientific Pandemic Influenza Group on Modelling (SPI-M), which advises the Government.

The authors of both papers stress that the rapid spread of Omicron could still lead to pressure on hospitals.

Scotland study

The University of Edinburgh study was based on hospital admissions of patients in Scotland, including those with the S gene negative signature of Omicron. Researchers calculated an adjusted observed/expected ratio of 0.32 (95% confidence interval [CI] 0.19–0.52) for Omicron, meaning that people who tested positive for the new variant were around 68% less likely to be hospitalised for 1 or more days than those with the Delta variant.

Evidence of vaccine protection against symptomatic Omicron infection after a booster dose was estimated at 57% (95% CI 54–60).

According to the study, the findings ‘should provide reassurance that Omicron is substantially less likely to result in severe outcomes than Delta’ and that booster, or third doses, of a COVID vaccine ‘are associated with considerable added protection against symptomatic disease when compared to second doses’.

However, the study involved only 15 patients hospitalised with Omicron and included few people over the age of 65, who are most at risk from COVID-19.

Dr Jim McMenamin, National COVID-19 Incident Director at Public Health Scotland, told a briefing hosted by the Science Media Centre that it was a ‘qualified good news story’.

However, he added: ‘The potentially serious impact of Omicron on a population can’t be underestimated. A smaller proportion of a much greater number of cases that may ultimately require treatment can still mean a substantial number of people who may experience severe COVID infections that could lead to potential hospitalisation.’

Commenting on the analysis, James Naismith, Professor of Structural Biology at the University of Oxford, said: ‘There is now solid reason to favour a more optimistic outcome of Omicron in the UK than was feared,’ while adding: ‘None of this should diminish the loss of lives that will still happen, nor the work of health professionals who are exhausted.’

England study

The new report from Imperial College London included all PCR-confirmed SARS-CoV-2 cases in England between 1 and 14 December. The dataset included 56,000 cases of Omicron and 269,000 cases of Delta.

On average, there was an estimated 15–20% reduced risk of attending accident and emergency departments for Omicron compared with Delta, and approximately a 40% lower risk of a hospital stay lasting at least 1 day, the researchers said.

However, the study said these reductions had to be balanced against the larger risk of infection by Omicron because protection from two doses of vaccine has waned.

Professor Neil Ferguson from Imperial, who led the study, said: ‘Our analysis shows evidence of a moderate reduction in the risk of hospitalisation associated with the Omicron variant compared with the Delta variant.

‘However, this appears to be offset by the reduced efficacy of vaccines against infection with the Omicron variant.’

Penny Ward, Visiting Professor in Pharmaceutical Medicine at King’s College London, said that, in England, ‘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’.

However, this should ‘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’, she said.

This article originally appeared on Medscape, part of the Medscape Professional Network.

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