Study estimates risk of Omicron causing severe disease

The Omicron variant of Covid-19 is less likely to cause hospitalization and severe disease than the variants that preceded it, according to a non-peer-reviewed study in South Africa, where the virus was first isolated.

Speaking during a news conference on Wednesday, Professor Cheryl Cohen of the country’s National Institute for Communicable Diseases (NICD), said their data supported initial observations that Omicron was less virulent than previous strains. 

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“In South Africa, this is the epidemiology: Omicron is behaving in a way that is less severe,” said Cohen, who also co-authored the study. 

The research, which has not yet been peer-reviewed, found that South Africans diagnosed with Omicron between October 1 and November 30 were 80% less likely to be admitted to hospital than people suffering from other variants of the virus during the same timeframe. 

The study also discovered that people hospitalized with Omicron in October-November were 70% less likely to develop severe symptoms than South Africans admitted to hospital with Delta between April and November.

The researchers prefaced their findings by noting that higher levels of community immunity, provided both by vaccines and through prior infection, likely played a part in limiting the severity of infection. 

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An estimated 60-70% of people in South Africa have already been infected with Covid-19, according to the NICD. “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,” they wrote. 

“Compellingly, together our data really suggest a positive story of a reduced severity of Omicron compared to other variants,” Cohen said in the press conference, adding that surveillance data suggests significantly lower hospitalizations and deaths in South Africa’s current Omicron-driven wave.

The Omicron variant has spread across the globe since it was first isolated by scientists in southern Africa in November. It has been responsible for soaring Covid-19 infections across the world and has demonstrated some capacity to evade the immune response provided by existing vaccines.