OMICRON is at least 2.4 times more likely to reinfect people who've already had Covid, scientists have revealed.
The variant has a "substantial" ability to swerve immunity in people previously infected with Covid, the first real-world study of the variant has found.
South Africa's National Institute for Communicable Diseases (NICD) warned their report has important public health implications as Omicron drives a huge spike in cases.
NICD data today showed 11,535 new Covid cases recorded in the last 24 hours, a surge of 368 percent from last Thursday's figure of 2,465.
Of the 51,402 people who took a Covid test a whopping 22.4 percent tested positive - up from 3.6 percent last Wednesday.
Only a quarter of people in South Africa are fully vaccinated, but previous waves of infection have built up natural immunity from previous Covid strains.
Gauteng province - where 80 per cent of people have tested positive for Covid previously - remains the epicentre of the explosion in cases.
Prior infection was previously thought to to cut the risk of catching Covid by around 80 per cent.
The NICD researchers said: "We find evidence of a substantial and ongoing increase in the risk of reinfection that is temporally consistent with the timing of the emergence of the Omicron variant in South Africa, suggesting that its selection advantage is at least partially driven by an increased ability to infect previously infected individuals.
"Immune escape from prior infection, whether or not Omicron can also evade vaccine derived immunity, has important implications for public health globally."
They added: "Urgent questions remain regarding whether Omicron is also able to evade vaccine-induced immunity and the potential implications of reduced immunity to infection on protection against severe disease and death."
NICD researchers say there were 35,670 reinfections in the 2,796,982 cases examined since last March.
The reinfection risk of Omicron was substantially higher than the Beta and Delta variants during the second and third waves, the study found.
Scientists from the NICD said data suggests Omicron may cause less severe illness than previous variants.
But many of the first cases have been in younger patients which could skew the data.
As Omicron spreads, hospitalisations in South Africa have rocketed by 180 per cent in the last week, with 98 Covid patients admitted last Thursday compared to 274 Covid today.
The NICD's Dr Michelle Groom said that scientists are examining the variant's possible immune escape.
She later tweeted: "Many cases are in younger age groups that are more likely to get mild disease.
"We need to wait and see how the variant behaves in other age groups.
Previous infection used to protect against Delta but now with Omicron that doesn't seem to be the caseAnne von Gottberg, microbiologist at South Africa's National Institute for Communicable Diseases (NICD)
"Also takes time for severe disease to manifest so we will know more in the coming weeks."
The World Health Organisation (WHO) has dispatched a team of experts to Guateng to help tackle the Omicron surge.
Anne von Gottberg, microbiologist at NICD, said around 75 per cent of samples sequenced are Omicron,
She said: "Previous infection used to protect against Delta but now with Omicron that doesn't seem to be the case."
But Barry Schoub, chair of the South African government's committee on COVID vaccines, told Sky News initial signs were "good".
He said: "Certainly, at this stage, the news does look to be promising - the great majority of the breakthrough infection (in other words, individuals that have had infection despite vaccination) is mild.
"Our hospital surveillance is showing a little bit of an uptick but certainly nothing as dramatic as we've seen in the previous waves."