Covid Scotland: Omicron hospital admissions lower than expected

Chris Robertson, professor of public health epidemiology at Strathclyde University, said the results were “astounding” but cautioned that there was still a high degree of uncertainty.

Covid cases have been on the rise in Scotland since November 27, but this has yet to translate into an uptick in hospital admissions.

Covid cases have been on the rise since November 27, but this is yet to be reflected in hospital admissions

During previous waves, most patients who required hospital treatment were admitted within five to 10 days of a positive test, but Prof Robertson stressed that the time lag may be longer with Omicron.

He said: “If it turns out that individuals with [Omicron] infections actually take a lot longer to go to hospital then we would be under-counting the eventual number at the minute."

Omicron cases confirmed through sequencing or probable/possible based on S-gene dropout in from cases in December and November respectively (Source: Public Health Scotland)

He added that there were still "very few" Omicron infections in Scotland among unvaccinated people and over-50s - particularly the elderly - who are both more likely to become seriously ill with the virus.

"If it turns out that when it does move into these groups, and people who are elderly with[Omicron] infection actually have a more severe infection then, again, our [modelling] counts will be an underestimate," said Prof Roberton.

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A third question is whether protection from boosters wanes in the same way as it does after a second dose.

Israel - which began administering boosters to over 60s at the end of July - is now set to offer them fourth doses in a bid to reduce hospital pressures from Omicron.

Prof Robertson said: "If it turns out there is a waning effect after the third dose that will also have implications, particularly if the waning is faster with Omicron relative to Delta."

Professor Chris Robertson

The EAVE II study fed in data on age, gender, deprivation, testing history, co-morbidities, and vaccine status among people who had tested positive for Omicron up to December 19 to calculate how many people should have become seriously ill, assuming the variant followed the same disease pattern as Delta.

Even after accounting for the fact that around half of cases were occurring in the 20-39 age group and that the vast majority of over-60s had been given boosters, the model still predicted that 47 patients should have ended up in hospital.

Prof Robertson said: "What we've got is 15 admissions. That's roughly a 70% reduction...what that tells us is we don't have as many admissions to hospital with Omicron as we were expecting had Omicron been exactly the same as Delta."

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The research also showed that patients who were double-vaccinated or had recovered from a prior Delta infection had much less protection against being infected by the Omicron variant than the Delta variant.

The Omicron variant is substantially more transmissible than Delta, but there has been mounting speculation that it may cause milder disease.

In South Africa cases have begun to dip following an exponential rise

Doctors in South Africa have reported that a much higher percentage of Covid patients during the Omicron wave have been asymptomatic - and admitted for other ailments - or treated without oxygen and ventilation.

However, just 6% of South Africa's population is over 65 compared to 19% in Scotland.

Prof Aziz Sheikh, who leads the EAVE II project at Edinburgh University, said: "We had concerns about how much we could infer from South Africa because there has been much greater natural exposure in South Africa and the age structure of the population is so different. But overall I think the fact that we're now seeing data from two countries pointing in the same direction is encouraging."

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There are still fears that the sheer transmissibility of Omicron - with warnings of a looming "tsunami" of cases - could far outweigh any benefits of milder disease.

Mark Woolhouse, professor of infectious disease epidemiology at Edinburgh University and a member of the SPI-M pandemic modelling group, said: "We're still at that paradox where individual infection - particularly in our well-vaccinated Scottish population - could be relatively mild for the vast majority of people. But the potential for all these infections to come along at once and therefore put serious strain on the NHS remains."

Dr Jim McMenamin, of Public Health Scotland, said it was a "important that we don't get ahead of ourselves", but welcomed an "important set of findings".

Hospital admissions with Covid, age standardised, per 100,000, by vaccination status (Source: Public Health Scotland)

It came as separate PHS data showed that 'boosted' individuals were 10 times less likely to be hospitalised with Covid than the double-jabbed in the week ending December 17.

The age-standardised hospitalisation rate was 2.8 per 100,000 for people given boosters or third doses; 29.7 per 100,000 for the double-vaccinated; and 34.5 per 100,000 for unvaccinated individuals.