Travelers receive COVID-19 tests ahead of their flights at a Histopath testing clinic at Sydney Airport in Sydney, Australia on December 7, 2021. The Omicron variant of COVID-19, first identified in southern Africa, has now been detected in countries from the US to Australia, underscoring the difficulties of curtailing contagious new strains. Photo: VCG

Australia had previously said it would offer the booster to everyone over 18 who had their second dose of the vaccine six months earlier.

But with rising cases of the Omicron variant, Health Minister Greg Hunt said the time interval will be shortened to five months after the second dose.

"A booster dose five or more months after the second dose will make sure that the protection from the primary course is even stronger and longer lasting and should help prevent spread of the virus," Hunt said in an emailed statement.

"Data from Israel shows boosters supporting reductions in the rate of infection in eligible age groups, severe disease in those aged over 40 years and deaths in those over 60 years."

Australia will use both vaccines from Pfizer and Moderna in its booster program.

Australia is one of the most vaccinated countries, with about 90 percent of people over 16 fully inoculated.

Still, Australia on Sunday reported 1,556 cases in the previous 24 hours as infections lingered near the six-week high reported a day earlier.

Australia has recorded about 229,000 COVID-19 infections, well below the toll of other nations, and 2,100 deaths.

The Omicron variant, first detected in southern Africa and Hong Kong, China in November, has triggered global alarm about another surge in infections. Cases have already been reported from Japan to the US and across Europe.