The illustration shows the response to an infection with Covid-19.
According to healthcare data from South Africa, the UK, and the Danes, a lower share of people with the Omicron coronaviruses variant are likely to require hospital treatment.
The researchers cautioned that Omicron's high degree of infectiousness could still strain health services despite the findings that there will be fewer cases of severe disease.
The reduction in severe illness was likely to be the result of Omicron's greater propensity to cause illness, compared with other variants, experts said.
The majority of Omicron infections are mild, so the proportion of cases that develop severe disease is lower than with other variants. The strain now accounts for a majority of Covid-19 cases in several countries.
An analysis of English data carried out by researchers at Imperial College found that Omicron was 11 percent less likely to produce severe disease in any given individual after adjusting for factors including age, sex, underlying health conditions, vaccination status and prior infections.
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The 25 percent reduction in the risk of hospitalization relative to Delta is due to the fact that Omicron cases are more likely than Delta cases to be among people who have been previously exposed to disease.
The South African study found that people who tested positive during October and November were less likely to be admitted to the hospital than people who tested negative. The data on prior infections were unreliable and researchers did not account for vaccination status in this analysis.
Omicron and Delta cases from recent weeks had the same likelihood of progressing to a serious condition, according to a second analysis from the same research team. More than 10,000 Omicron cases and 200 hospital admissions were included in the analyses.
Prof. Cheryl Cohen is an epidemiologist at the University of Witwatersrand and one of the study's authors.
She said the findings suggested that Omicron was less severe because of the immune protection from T-cells and B-cells.
