The Omicron variant of Covid-19 has led to far less hospital admissions and severe illness among people infected with the virus in South Africa to date than the earlier Delta variant, a new study has found.
Scientists from South Africa’s National Institute for Communicable Diseases (NICD) and local universities say the milder infections associated with Omicron locally may be down to a number of reasons, with immunity among infected people high among them.
Omicron was first identified by scientists in South Africa's Gauteng province in early November, and the variant is suspected of driving the fourth wave of coronavirus that has swept the nation in recent weeks due to its high transmissibility levels. It has since moved rapidly across the globe.
The South African Omicron study’s authors on Wednesday confirmed that the new variant has now replaced Delta as the dominant strain of the virus locally, saying it currently accounts for over 95 per cent of new recorded infections.
The study was conducted by comparing data on its infections in October and November with data on Delta infections from April to November.
The researchers found the risk of hospital admission was roughly 80 per cent lower for those infected with Omicron compared with Delta, and that the vast majority of those needing medical care were unvaccinated.
They also confirmed the increased transmissibility of the new variant, saying people infected with Omicron have a significantly higher viral load in the nose than those with Delta.
While the study has yet to be peer-reviewed, its results have been cautiously welcomed in South Africa.
Range of factors
However, the scientists involved have warned against using their findings to jump to conclusions about Omicron’s underlying characteristics, saying the reduced severity of illness associated with it was likely due to a range of factors.
"We can't tell from this data how much is from vaccination, previous infection or the intrinsic reduced virulence of the virus," said Prof Cheryl Cohen, who leads the NICD respiratory diseases unit.
“However, in South Africa Omicron is behaving in a way that is less severe and this is likely to be the same in sub-Saharan African countries with similar very high levels of previous infection.
Prof Cohen said it was unclear whether the situation encountered in South Africa would be similar in countries with high levels of vaccination but very low levels of previous infection.
Dr Michelle Groome, head of public health, surveillance and response at the NICD, said South Africa was likely only diagnosing a small fraction of the people who have contracted Covid-19 because so many are asymptomatic.
However, she said that seroprevalence studies showed that “in excess of 70 per cent of South Africans have been exposed and have underlying immunity to Covid-19”, which meant the population’s immune effect was likely kicking in.
The World Health Organisation said on Wednesday it did not yet have enough data on the Omicron variant to say if it was more or less severe than the Delta variant.
“We do have some data suggesting that rates of hospitalisation are lower,” the WHO’s technical lead on Covid-19, Maria van Kerkhove, said in a briefing with media. But she cautioned against drawing conclusions from the early data because “we have not seen this variant circulate long enough in populations around the world, certainly in vulnerable populations”.
