The highly contagious Omicron variant of SARS-CoV-2, has significantly increased the number of people reinfected with Covid, unlike previous variants, experts contended in an article on Nature. A recent study by the Imperial College London has shown that the risk of reinfection with the Omicron coronavirus variant is more than five times higher than other strains. Researchers at Deakin University in Australia's Melbourne stated that the first signs of Omicron's immune-evasive properties came from data collected in South Africa.
In November last year, South African researchers showed higher than expected rates of reinfection compared with those of previous waves. Similar trends have now been documented elsewhere.
Data collected by the UK Health Security Agency showed that more than 650,000 people have probably been infected twice in England, and most of them were reinfected in the past two months, the report said.
Before mid-November, reinfections accounted for about 1 per cent of reported cases of Covid-19, but the rate has now increased to around 10 per cent.
Understanding reinfection rates is crucial for assessing "how infections might surge and if hospitals will be able to cope", Catherine Bennett, an epidemiologist at Deakin was quoted as saying.
Further, the UK Office for National Statistics in Newport has also seen a sharp increase in possible reinfections in recent months, as part of its random sampling of households across the country.
The survey counts a possible reinfection if four months have passed since the previous one.
It found reinfection risk was 16 times higher between mid-December last year and early January this year when Omicron dominated, than in the 7 months leading up to December when Delta was the dominant variant.
Such surveys could be underestimating the true rate of reinfection because some infections go undiagnosed, and some could have happened sooner after the first infection - especially in countries where cases of Omicron quickly followed a Delta wave, Bennett said.
So what is causing the reinfection? According to Bennett, multiple factors could explain the spike in reinfections.
With more people now already exposed to the virus, there is a higher chance of seeing reinfections, she explained. Omicron's speedy spread also increases the chance. But the variant's ability to evade immunity is probably playing a part, Bennett was quoted as saying.
According to the experts, the recent surge in Covid cases driven by the highly contagious Omicron is because of its ability to evade the body's immune defences.
Several studies have shown that the variant can outwit immunity induced by vaccination as well.
To understand how far Omicron can evade immunity, a team of researchers at Weill Cornell Medicine, Qatar in Doha, conducted a nationwide study.
Their findings published in The New England Journal of Medicine this month, showed that although having previously been infected was around 90 per cent effective at preventing an infection with the Alpha, Beta or Delta variants, it was only 56 per cent effective against Omicron, the report said.
However, most reinfections occurred about one year apart, showing that a previous infection offers immunity for some time.
And protection against severe Covid-19 caused by Omicron remained high, at around 88 per cent.
But Shabir Madhi, a vaccinologist at the University of the Witwatersrand in Johannesburg, South Africa, was quoted as saying that the study probably missed many infections that were asymptomatic or mild and were therefore not recorded. So it might be overestimating the effectiveness of a previous infection against Omicron.