It’s expected the BA.5 variant will soon be dominant, leading to many re-infections, an infectious diseases physician says

Australians should brace for a fresh wave of COVID-19 infections this winter as a new variant of concern is on the verge of becoming dominant in the most populous state, experts warn.

A NSW respiratory surveillance report indicates the prevalence of the Omicron subvariant BA.5 has “increased substantially”, making up nearly a quarter of COVID-19 infections that underwent genome sequencing last week.

“It is expected that BA.4 and BA.5 will become the dominant strains and will likely be associated with an increase in infections in the coming weeks,” the report states.

Infectious diseases physician Associate Professor Sanjaya Senanayake, from ANU’s medical school, says a similar trend could occur nationally, with many millions of Australians who contracted Omicron earlier this year not necessarily protected against the BA.4 or BA.5 subvariants.

“So you’ll see people who had infections a few months ago suddenly getting COVID again and that’s because with BA.4 or BA.5, the antibody responses aren’t as strong.”

Overseas, the US Centers for Disease Control and Prevention has reported a similar trend, with BA.4 and BA.5 now accounting for more than 21% of new cases in the US, while the new subvariants are also driving infections in the UK and Europe.

An analysis from Imperial College London found that Omicron infection provided a poor immune boost against re-infection with Omicron itself, even in the triple-vaccinated.

Meanwhile, preliminary data from the University of Tokyo suggest the subvariants might have evolved to act similarly to earlier variants, such as Alpha and Delta, by infecting the lung tissue rather than the upper respiratory tract like previous Omicron variants.

Professor Senanayake cautions it is too early to know whether that would translate to an increase in severe disease and hospitalisations in Australia.

“It may also be that even though the antibody responses aren’t so strong, the T-cell activity from vaccines and previous infection might still protect us from severe disease.

“Only time will tell.”