Omicron sub-variants BA.4 and BA.5 have the ability to avoid immunity induced by both previous COVID infection and vaccination, according to a new study not yet peer-reviewed.

According to researchers from the Africa Health Research Institute in South Africa, the findings could signal a fresh wave of infections by the BA.4 and BA.5, Bloomberg reported. Last month, scientists at the Centre for Epidemic Response and Innovation (CERI) in South Africa detected the two new sub-variants of the highly contagious Omicron variant.

In a series of tweets, Tulio de Oliveira, Director of CERI, revealed that "BA.4 and BA.5 are distinct from other Omicron lineages". "BA.4 and BA.5 are estimated to have originated in mid-December 2021 and early January 2022, respectively."

Besides seven provinces in South Africa, the sub-variants have also been detected in more than 20 countries including Australia, Austria, Belgium, China, Israel, Denmark, France, Germany, Pakistan, the UK, US and Switzerland, de Oliveira wrote on Twitter.

In the pre-print study, researchers at the Institute analysed blood samples from unvaccinated 24 people infected with the original Omicron variant. The team also tested the sublineages against samples from 15 vaccinated people, eight of whom had Pfizer shots and seven who had received Johnson & Johnson's vaccines.

The findings showed an almost eight-fold drop in neutralising antibody production when tested against the BA.4 and BA.5 sublineages, the Bloomberg report said. Samples from people who were vaccinated showed about a threefold decrease, according to the study.

"The low absolute neutralisation levels for BA.4 and BA.5, particularly in the unvaccinated group, are unlikely to protect well against symptomatic infection," the researchers said in the study. "This may indicate that, based on neutralisation escape, BA.4 and BA.5 have the potential to result in a new infection wave," they added.

The study comes amid a fresh surge of infections in South Africa, where Omicron was first identified in the country along with neighbouring Botswana in November last year. On April 30, South Africa recorded 6,527 new cases and a test positivity rate of 21.5 per cent, compared with 581 cases and a positivity rate of 4.5 per cent on March 28.

While hospitalisations are rising gradually, there hasn't been a noticeable increase in deaths, Waasila Jassat, a public health specialist at South Africa's National Institute of Communicable Diseases, was quoted as saying.