Key Points
- XBB and BQ.1 can escape immunity from past infection and vaccination: Victorian Chief Health Officer
- New variants don't cause severe illness than other Omicron subvariants: WHO
- Vaccines still work but may have reduced protection against new subvariants: WHO
Most Australian states and territories reported a rise in new weekly COVID-19 cases for the week ending 28 October.
Tasmania reported the highest increase at 30 per cent.
It was followed by the Australian Capital Territory (26. 25 per cent), Victoria (24.4 per cent), Western Australia (18 per cent), New South Wales (13 per cent) and South Australia (10 per cent).
Victorian Chief Health Officer Brett Sutton said XBB and BQ.1 now constitute about 10 per cent of the total cases in the state and could overtake the dominant BA.5 subvaraint.
"These indicators (combined with an eight per cent increase in antiviral prescriptions) show we are at the start of another COVID-19 wave," Mr Sutton said on Friday.
He said these variants are driving significant case and hospitalisation waves overseas due to their ability to escape immunity from past infection (including BA.5) and waning immunity from past vaccination.
NSW Health said it was also closely monitoring the emergence of XBB and BQ.1 and other international and local data to assess the growth potential of the new variants.
What are XBB and BQ.1. subvariants?
XBB is a recombinant of BA.2.10.1 and BA.2.75 sublineages. It has a global prevalence of 1.3 per cent and has been detected in 35 countries.
BQ.1 is a BA.5 subvariant with a global prevalence of six per cent. It has been found in 65 countries.
Severity
Epidemiologist Catherine Bennett said these subvariants are not appearing to be causing more severe illness.
"But the concern is that they are different enough (from other Omicron subvariants) to have some immune escape properties," Professor Bennett told SBS.
"This means that a recent infection with another Omicron variant might not provide the same level of protection against reinfection. "
Deakin University chair of epidemiology Professor Catherine Bennett. Source: Supplied / Supplied by Professor Catherine Bennett
The current data do not suggest substantial differences in disease severity for XBB infections
"There is early evidence pointing at a higher reinfection risk than other circulating Omicron sublineages. Cases of reinfection were primarily limited to those with initial infection in the pre-Omicron period."
The WHO said BQ.1 shows a significant growth advantage over other circulating Omicron sublineages in Europe and the US and warrants close monitoring.
A higher reinfection risk is a possibility that needs further investigation.
"However, at this time, there is no epidemiological data to suggest an increase in disease severity," it said.
Are current vaccines effective against new subvariants?
The WHO said protection from vaccines, including bivalent, may be reduced. Still, no significant impact on protection against severe disease is foreseen.
Prof Bennett said it's important for everyone to take recommended boosters, especially those over 50 or with underlying medical conditions.
"Boosters have been shown to provide some short-term protection against getting infected," she said.
Global XBB and BQ.1 waves
Prof Bennett said these variants have resulted in a spike in new cases, but not like the previous waves.
"France had the highest rates of BQ.1 in early October, and it looks like their hospitalisations are already starting to decline, so that's encouraging," she said.
"Same in Singapore with XBB."
Protection and preventive measures against new subvariants
Prof Bennett said the chances for a new wave reduces when people socialise more outdoors.
Professor Sutton reminded residents that vaccination, masks, ventilation, testing, staying home when sick and COVID-19 treatments are highly effective at reducing transmission and illness.
"If you don't test, you can't access important oral treatments, including antivirals," he said.
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