The Omicron variant is more likely to cause Covid-19 re-infection compared to the Delta and Beta variants.
A study conducted by South African scientists that is yet to be peer-reviewed has shown that the Omicron variant can still infect people who have acquired immunity from previous Covid-19 infection.
But the scientists say the symptoms of re-infected patients, just as those who are vaccinated, are mild.
“Omicron variant is associated with substantial ability to evade immunity from prior infection. In contrast, there is no population-wide epidemiological evidence of immune escape associated with the Beta or Delta variants,” said the study.
Immune escape means that a person’s ability to fight an infection because of their body’s natural immune response or using vaccine immunity is no longer viable, or, it has waned. Of note is that an infection that occurs after one is vaccinated is called a breakthrough infection.
The researchers analysed their data by looking at the trends of primary (or first time) infection and compared it with that of second time infections.
Their graph shows that the reinfection rate peaked in October, a few weeks before cases of the Omicron variant were reported in southern Africa.
“Since early October, we see a decreased risk of primary infection, though this could be partially explained by vaccine rollout. We see a simultaneous increase in reinfection risk,” explained Dr Juliet Pulliam, who was part of the study, in a tweet.
She explains that, of the reinfections that they have analysed, most are from people who tested positive for Covid-19 way before the Omicron variant was reported, and that a number of the reinfections are from people who previously had the Delta variant.
“These findings suggest that Omicron’s selection advantage is at least partially driven by an increased ability to infect previously infected individuals,” tweeted Dr Pulliam.
The researchers have been monitoring the trend since January 2021 and while the study is still in pre-print, the Omicron variant re-infection rate has raised a brow.
The study did not focus on breakthrough infections as the researchers did not have information about the vaccination status of the samples they tested.
“We cannot make any assessment of whether Omicron also evades vaccine-derived immunity,” explains Harry Moultrie, a senior epidemiologist who was also part of the study.
“Immune escape from prior infection, whether or not Omicron, can also evade vaccine derived immunity, has important implications for public health globally, but there is still a lot we don’t know,” adds Dr Pulliam.
Monitor immune escape
A separate study published by the scientific journal Frontiers in Immunology says that scientists should take a keen interest in the upcoming variants and monitor their immune escape which will inform an update of the available vaccines.
“The number of people with acquired immunity against Covid-19 continues to increase after natural infection or vaccination, but due to unequal interventions and access to vaccines, the virus would subject to greater immune pressure and require repeated immunisation rounds to deal with the continuous arising of virus variants,” says the Frontiers study.