The increased demand follows the federal government's decision to reduce the recommended waiting period for the booster shot from six months to five months, a decision which caused the number of Victorians overdue for their booster vaccine to rise to nearly 450,000.

UFS chief pharmacist Peter Fell said all available vaccination bookings through UFS pharmacies had since been booked, while the UFS vaccination clinic in Dana Street had reportedly also reached capacity.

"They've gone from having very low numbers to having to cancel walk-ins," Mr Fell said.

"And in the case of our 24-hour pharmacy, I believe they're booked through to the end of February now."

Mr Fell said the present inability to meet local patient demand was not a vaccine supply issue as such, but instead a problem referable to ordinary supply-chain issues.

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"It's always about a two-week turnaround from the time you order [the vaccine] to when you receive it," he said.

"So, when we're caught unawares with an announcement like this, it will inevitably take a couple of weeks just to mobilise vaccine supplies."

Beyond that, Mr Fell said the roll-out of booster shots - at least in the case of pharmacists - was being hampered by an acute labour shortage.

"At least for the UFS, workforce capacity is proving a bigger problem than concerns around funding," he said.

The difficulties meeting patient demand come amid a warning from the Australian Medical Association that the national booster program is already dangerously lagging relative to the threat posed by the Omicron strain.

Contrary to early indications, the most recent international research on the Omicron variant suggests a third vaccine dose is in fact required to protect against the risk of serious symptomatic disease.

In individuals vaccinated with Astra Zeneca, the findings of the study showed the Omicron variant effectively reduced vaccine effectiveness to zero four months after a person's second dose. In the case of the Pfizer vaccine, vaccine effectiveness was shown to decline from 80 per cent to 35 per cent in the same period.

The AMA said the roll-out of the booster program needed to be sped up to combat the risk to the community posed by the Omicron variant.

It also said the closure of a number of state-run vaccination hubs in recent weeks had effectively shifted the burden of delivering the booster program to GPs and pharmacists.

AMA president Omar Khorshid said this was problematic given the marked decline in federal government funding for GPs and pharmacists involved in the delivery of booster program.

"[The Commonwealth funding cut] is making it very difficult for GPs to run clinics at the volume and scale required," Dr Khorshid said. "GPs and pharmacists are not being properly supported to implement this critical booster program."

According to the AMA, only 251,000 booster shots were delivered through GPs and pharmacists last week, compared to 975,000 vaccine doses each week two months ago.

Meanwhile, over four million Australians are now due for their booster shot.

The AMA has called for the re-opening of all state-run vaccination hubs as well as the restoration of federal government funding to support the delivery of the booster program.

The Victorian government recently announced 10 pop-up vaccine clinics to assist with the increased demand.