Federal Health Minister Greg Hunt says booster shots will become an essential way to protect Australians against Covid-19, particularly in the face of the new, highly infectious Omicron variant spreading around the world.

Speaking after receiving his third AstraZeneca shot alongside health department secretary Brendan Murphy, Mr Hunt said 1.5 million more Australians were now immediately eligible for a booster after ATAGI brought forward the wait time from six to five months.

He also confirmed the Moderna jab will join the nation's booster program.

“With one of the highest vaccination rates in the world, with one of the lowest rates of loss of life and one of the strongest economic recoveries, Australia is doing incredibly well, but the shorter time for boosters, the extra booster option with Moderna which Brendan and I have had today, gives Australians more access, earlier access, and more confidence that despite all of the challenge we’ll get through it," he said.

When asked why ATAGI had changed its advice since last week, Mr Murphy said emerging international evidence had found protection from vaccinations waned before the six month mark.

"What has changed in the last week is that ATAGI has had access to what we call the laboratory in-vitro neutralisation data which is a complicated way of saying tests in the lab to see how the immunity from the primary vaccination declines over time, particularly in relation to Omicron," he said.

"There's evidence that by six months there is some declining protection to Omicron and so ATAGI felt that there was a good reason to get people boosters if possible before that 6-month mark so they felt bringing it forward to five months was worth doing."