Associate Professor Stuart Turville from the UNSW's Kirby Institute says Omicron subvariants BA.2.12.1, BA.4 and BA.5 have been detected in Australia.
Authorities are warning this winter season is likely to see a spike in COVID-19 cases and flu as restrictions which have suppressed the circulation of both viruses are phased out.
The latest advice from the Australian Technical Advisory Group on Immunisation recommends people wait three months after a confirmed COVID-19 infection and then receive their next vaccine dose as soon as possible.
The advice, issued last week, applies to all people and for all COVID-19 vaccines.
Prof Turville said the severity and transmissibility of the new Omicron subvariants had yet to be determined.
The arrival of Omicron BA.1 and BA.2 were marked by their ability to significantly evade a previous antibody response through past infection and/or vaccination, but the impact was less severe.
The new subvariants BA.4, BA.5 and BA2.12.1 are likely to displace BA.1 and BA.2 in Australia.
"We will need to study this over time to see if their advantage is one of "fitness/transmissibility" and/or their ability to be more slippery to existing antibodies," Prof Turville said.
"As with all variants, the key parameter to watch is disease severity and this data takes time to accumulate.
"There is still a lot about this virus that is unknown and there are many paths it has the potential to take."