A smaller proportion of people are infected Omicron is a variant of the coronavirus will likely require inpatient treatment compared to Delta strain cases, according to health data from South Africa, Denmark and the UK.
The findings of separate research teams raise hopes that there will be fewer cases of severe disease than those caused by other strains of the virus, but researchers have warned that Omicron’s high level of infectivity could continue to burden health services.
The reduction in severe disease probably stems from Omicron’s greater propensity, compared to other variants, to infect people who have been vaccinated or previously infected, experts said, although British studies have also hinted at a possible drop in intrinsic weight.
Unvaccinated groups remained the most endangered, but as the vast majority of penetrating infections and reinfections caused by Omicron are mild, the proportion of all cases that developed severe disease is lower than in other variants. This strain now accounts for the majority of Covid-19 cases in several countries, including the United States.
An analysis of English data from researchers at Imperial College found that Omicron was 11 percent less likely to cause serious illness in any individual after adjusting for factors including age, gender, underlying health conditions, vaccination status and previous infection.
At the population level, this has reduced the risk of hospitalization by 25 percent compared to Delta, with a steeper decline due to the fact that Omicron cases are more likely than Delta cases to be among people previously infected or vaccinated, providing significant protection against severe diseases.
A South African study conducted by the National Institute of Infectious Diseases found that among people who tested positive during October and November, suspicious cases of Omicron were 80 percent less likely than Delta cases to be admitted to hospital, after adjusting to various factors including previous infection. But the researchers stressed that they did not take vaccine status into account in this analysis, and data on previous infections were unreliable.
Another analysis by the same research team, this time checking vaccination status, showed that, after being admitted to hospital, the Omicron and Delta cases from recent weeks were equally likely to progress to a serious condition. The analyzes included more than 10,000 Omicron cases and more than 200 hospital admissions.
“Something is happening. . . in terms of the difference in immune response for Omicron against Delta, ”said Professor Cheryl Cohen, an epidemiologist at the University of the Witwatersrand and one of the study’s authors.
She said the findings suggest that breakthrough infections and reinfections from Omicron were “less severe” and that immune protection from T-cells and B-cells “mediated” Omicron’s “progression to severe disease” despite declining antibody protection.
Cohen said the reduced hospital load has allowed South Africa to cope with the Omicron wave without imposing isolation, but warned that the findings may not apply to western countries with older populations.
“It’s about what [Omicron] it means in terms of absolute numbers because, if the numbers are so high, it can still cause a significant public health problem even if the risk of serious illness is lower per case, ”she added.
Separately, Danish data showed that among people who tested positive between November 22 and December 15, Omicron cases were three times less likely to be admitted to hospital than cases with other variants. But experts have warned that the concentration of Omicron outbreaks among younger groups could skew the data.
“Omicron primarily affects young and vaccinated people, and when we adapt, we see no evidence that Omicron should result in a milder disease,” said Henrik Ullum, director of the Statens Serum Institute, a Danish public health agency, at a news conference in on Wednesday.
But while there is still limited evidence for any intrinsic reduction in severity, this does not rule out that Omicron results in less serious outcomes at the population level, due to a higher proportion of cases among people with some protection against severe disease either previous infection or vaccination.
“Because of Omicron’s greater immune evasion, this pattern [of fewer cases being hospitalised] will persevere in population-based assessment, ”said Prof. Samir Bhatt, Professor of Machine Learning and Public Health at the University of Copenhagen and a member of the SPI-M UK Government Modeling Group.
The UK government is awaiting new information on the seriousness of Omicron before deciding on further restrictions in England. But Bhatt said Britain’s approach was “Panglossian”, adding that he “overestimated the hope offered by reduced seriousness”.
“I feel that the rise in hospital pressures will be slower and smaller because the vaccine still seems to be protecting,” said Professor Thea Kolsen Fischer, head of specialist virus diagnostics and microbiology at the Statens Serum Institute.
But she added that policymakers should be “a little wary of making the narrative milder” because it will be “a week” before the impact of the variant on hospitals becomes clear.
“I’m afraid it’s because of Omicron’s contagion. . . what we see now will be very different in just two weeks, ”she said.
Denmark introduced a series of crackdown measures on Sunday Omicron’s spread, including the closure of theaters and museums and capacity constraints in bars, restaurants and shopping malls.
Professor Peter Garred, a clinical immunologist at Copenhagen’s Rigshospitalet, Denmark’s largest hospital, said a drop in severity could lead to a decision by countries such as England and the United States not to impose restrictions on “roughly sustainable”.
“The question of whether Omicron is mild or not is not actually included in the discussion of the new restrictions [in Denmark]Said Garred. “The government is predicting problems because infection rates are rising so dramatically, no matter how serious.”
Cohen of the University of the Witwatersrand said the Omicron wave could “move differently” in the northern hemisphere because it coincides with winter, but added that positive signs from South Africa were “of great importance to other countries and how they react.”
“Most populations have a previous infection or vaccination or both at this time,” Cohen said. “If it lasts, it’s probably true that all countries will see a similar effect as we do.”