South African Study: Omicron Variant Has Lower Risk Of Hospitalization And Severe Illness Than Delta Variant

JAKARTA - A South African study showed a reduced risk of hospitalization and severe illness in people infected with the Omicron variant of the coronavirus compared to the Delta variant, although the authors say some of this may be due to the population's high immunity.

The question of Omicron's virulence is at the heart of the scientific and political debate in many countries, as governments grapple with how to respond to the spread of the variant as researchers race to understand it.

The study, which has not yet been peer-reviewed, found people diagnosed with Omicron in South Africa between October 1 and November 30, were 80 percent less likely to be hospitalized than those diagnosed with the other variant over the same period.

Among patients treated during that period, those with the Omicron variant had the same chance of developing the severe disease as those with the other variant.

However, the study found people who were hospitalized with the Omicron variant in October-November were 70 percent less likely to develop the severe disease than those treated with the Delta variant between April and November.

"Interestingly, together with our data really do show a positive story about decreasing severity of the Omicron variant compared to other variants," said Professor Cheryl Cohen of the National Institute for Infectious Diseases (NICD), one of the writers of the study, as quoted by Reuters, December 22.

He said this was further corroborated by surveillance data showing significantly lower hospitalizations and deaths in the current Omicron-driven wave of infections in South Africa than in previous waves, although the number of cases was much higher.

Cohen said the study's findings could likely generalize to other countries in sub-Saharan Africa that also have very high rates of prior infection.

"What is not clear is whether the picture will be similar in countries where there are high vaccination rates but very low rates of prior infection," he said during a media briefing by a group of NICD scientists.

The study was carried out by a group of scientists from the NICD and major institutions including the University of the Witwatersrand and the University of KwaZulu-Natal.

The authors include several caveats and caution against jumping to conclusions about Omicron's intrinsic characteristics.

"It is difficult to disentangle the relative contribution of previously high levels of population immunity, versus lower intrinsic virulence to the observed lower disease severity," they wrote.

An estimated 60 percent to 70 percent of people in South Africa have had a previous COVID-19 infection, Cohen said.

Separately, Paul Hunter, a professor of medicine at the British University of East Anglia, described the South African study as important and said it was the first properly conducted study to appear in the preprinted form on the problem of the severity of the Omicron variant versus the Delta variant.

But, Hunter said comparing Omicron-variant data from one period with Delta-variant data from an earlier period, meant it was difficult to determine whether the lower hospitalization rates were due to the less virulent Omicron or to increased population immunity.

"To some extent this is not a problem for patients who only care that they will not become seriously ill. But it is important to know to allow for a better understanding of the possible pressure on healthcare," he said.

To note, the results of a large study by Imperial College London released last week showed no sign of the Omicron variant being milder than the Delta variant, although hospitalization data are still very limited. It has not been peer reviewed and published in a medical journal.