Covid: Omicron is 80 PER CENT less likely to cause hospital admission than Delta, study suggests

People who catch Omicron are 80 per cent less likely to be hospitalised than those who get Delta, a major study from South Africa suggests.

The real-world analysis, of more than 160,000 people, comes ahead of a similar UK Government report expected to show Britons are also less likely to be severely ill with the variant. 

Omicron sufferers were also 70 per cent less likely to be admitted to ICU or put on a ventilator compared to those with Delta, according to the study led by South Africa's National Institute for Communicable Diseases (NICD). 

South African doctors have insisted for weeks that Omicron is milder since raising the alarm about it on November 24 and accused the UK of panicking about Omicron.

But the researchers at the NICD who carried out the study, which has not been peer-reviewed yet, said it still doesn't answer whether Omicron is intrinsically weaker than Delta.

'It is difficult to disentangle the relative contribution of high levels of previous population immunity versus intrinsic lower virulence to the observed lower disease severity,' the researchers concluded. 

Built-up immunity from three previous waves of the virus and vaccines are believed to be doing most of the heavy lifting in keeping patients out of hospital this time around.

Up to 70 per cent of South Africans are believed to have had Covid before and only around a quarter are double vaccinated, with boosters not widely available yet.  

The findings will raise hope that the UK also face a much milder wave, with 75 per cent of the population double-jabbed and nearly half boosted.

Boris Johnson is said to have held fire on bringing in more Covid restrictions ahead of Christmas after the UK Health Security Agency tentatively backed suggestions that Omicron infections tend to be less severe, boosting hopes that the coming weeks may not be as bad in terms of case numbers and hospitalisations as experts have previously forecast.

A UKHSA spokesperson said: 'We are reviewing all analyses continuously to help inform the pandemic response, which includes assessing the severity of Omicron. We will publish these latest findings in the variant technical briefing on December 23.' 

Omicron cases in South Africa yesterday fell for the fourth day in a row, while the UK's daily cases have been flat at around 90,000 for six days.

South Africa's hospital admissions are hovering at below 400 per day, on average, and dropped by 5 per cent in a week yesterday. In the UK, hospital rates have been mostly flat since late summer, with around 900 per day. 

That's despite gloomy Government modelling warning that 1million Britons could be catching the virus daily by the end of the year.

Their study, which has not been peer-reviewed and was published on pre-print website medRxiv , found that among the 10,547 Omicron cases identified between October 1 and November 30, 261 (2.5 per cent) were admitted to hospital. For comparison, among the 948 non-Omicron cases in the same period - almost all of which would have been Delta, which was behind 95 per cent of cases before Omicron emerged - 121 people were hospitalised (12.8 per cent). The researchers said shows that those who caught Omicron had a 80 per cent lower risk of requiring hospital care

Professor Paul Hunter, an expert in infectious diseases at the University of East Anglia, described the South African study as important and said it was the first properly conducted study to appear in pre-print form on the issue of Omicron versus Delta severity.

But Professor Hunter said its main weakness was that it compared Omicron data from one period with Delta data from an earlier period.

'So even though cases of Omicron were less likely to end up in hospital than cases of Delta, it is not possible to say whether this is due to inherent differences in virulence or whether this is due to higher population immunity in November compared to earlier in the year,' he said.

'To a certain extent this does not matter to the patient who only cares that they won't get very sick. But it is important to know to enable improved understanding of the likely pressures on health services.'

The analysis was carried out by a group of scientists from the National Institute for Communicable Diseases (NICD) and major universities including University of the Witwatersrand and University of KwaZulu-Natal.

They used data from four sources: national COVID-19 case data reported to the NICD, public sector laboratories, one large private sector lab and genome data for clinical specimens sent to NICD from private and public diagnostic labs across the country.

They compared data on Omicron infections in October and November with data about Delta infections between April and November, all in South Africa.

A case was considered to be Omicron if the positive test did not detect part of the virus' cell - a tell-tale signal for Omicron due to its extensive mutations - and a high amount of the virus in the sample.

And a hospitalisation was linked with a positive case if a person was admitted to hospital between seven and 21 days of testing positive.

A patient was considered to have severe disease if they were admitted to ICU, required mechanical ventilation, received an oxygen treatment, fluid leaked into their lung or died.

Their study, which has not been peer-reviewed and was published on pre-print website medRxiv, found that among the 10,547 Omicron cases identified between October 1 and November 30, 261 (2.5 per cent) were admitted to hospital.

For comparison, among the 948 non-Omicron cases in the same period - almost all of which would have been Delta, which was behind 95 per cent of cases before Omicron emerged - 121 people were hospitalised (12.8 per cent).

After adjusting for other factors, the researchers said shows that those who caught Omicron had a 80 per cent lower risk of requiring hospital care.

Among those hospitalised with either strain in the nine-week period, the severity of illness was the same, with 317 of the 382 patients (83 per cent) discharged by December 21.

But comparing Omicron hospitalisations with Delta hospitalisations earlier this year, the scientists found Omicron patients were less likely to suffer from severe disease.

Since the beginning of the pandemic, 1,734 people in South Africa have been hospitalised whose test was genomically sequenced as either Alpha, Beta, Delta or Omicron. 

The researchers also found that Omicron patients had much higher viral loads compared to Delta infections, echoing recent studies and data that the strain is more transmissible.

The researchers noted that around seven in 10 South Africans had already been infected with Covid by November when Omicon hit, while a quarter of its population is double-jabbed.

It is 'difficult to disentangle' how much previous infection and vaccines contribute to high levels of immunity against hospitalisation and severe illness from Omicron and how much is due to Omicron itself being less severe, the experts said.

Because there is no difference in Covid severity among Omicron and Delta patients hospitalised in the last two months, it is likely that the reduced severity of Omicron 'may be in part a result of high levels of population immunity' due to previous infection or vaccination, the researchers said.

In a separate study, officials who looked at 78,000 Omicron cases in the past month found the risk of hospitalisation was a fifth lower than with Delta (in green) and 29 per cent lower than the original virus (dark blue). Omicron is shown in brown and the original South African 'Beta' variant in light blue. Children appeared to have a 20 per cent higher risk of hospital admission with complications during the new wave than the initial outbreak, despite the numbers still being tiny

As a crude rate, Omicron is currently causing a third fewer hospital admissions than Delta did during its entire wave — 38 admissions per 1,000 Omicron cases, compared to 101 per 1,000 for Delta 

'The high population immunity (due to prior infection and/or vaccination) may be protective against severe disease in our population,' the team wrote.

The scientists noted their results should be 'interpreted with caution' because the study took place early in the Omicron wave when 'patients with milder symptoms were more likely to be admitted' and only included individuals where information was recorded during their stay, which may have been biased towards patients with shorter hospital stays.

Professor Paul Hunter, a professor of medicine at the University of East Anglia who was not involved in the study, said the findings are the first properly conducted study to examine Omicron's severity against Delta.

But he said its main weakness is that it compared Omicron data from one period with Delta data from an earlier period.

Professor Hunter added: 'So even though cases of Omicron were less likely to end up in hospital than cases of Delta, it is not possible to say whether this is due to inherent differences in virulence or whether this is due to higher population immunity in November compared to earlier in the year.

'To a certain extent this does not matter to the patient who only cares that they won't get very sick. But it is important to know to enable improved understanding of the likely pressures on health services.'

It comes after a separate real-world study of 78,000 Omicron cases in South Africa found the risk of hospitalisation was a fifth lower than with Delta and 29 per cent lower than the original virus.

As a crude rate, Omicron is led to a third fewer hospital admissions than Delta did during its entire wave — 38 admissions per 1,000 Omicron cases compared to 101 per 1,000 for Delta.

The study also found two doses of Pfizer's vaccine still provide 70 per cent protection against hospital admission or death from Omicron, compared to 93 per cent for Delta.

While this is more protection than many scientists initially feared, it still leaves 30 per cent of people vulnerable to severe Omicron disease, four times as many as Delta.

Waning immunity from two Pfizer doses was found to offer just 33 per cent protection against Omicron infection, explaining why the country has seen a meteoric rise in case numbers.