Premier Daniel Andrews said on Wednesday the change would be effective immediately.

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"If you've had your second dose within the last three months, then you will now be eligible - that is if three months have passed since your second dose of the COVID-19 vaccine, you will be eligible for a third dose," he said.

"That interval has been reduced down to three months effective immediately."

The reduced timeframe will mean 1.2 million more Victorians can now increase their immunity before school and work returns in full.

It is not the first time the interval between second and third dose has been reduced.

Mr Andrews also announced a 'booster blitz' weekend this coming Saturday and Sunday, where additional capacity will be added to state vaccination hubs, longer open hours, and in many cases, walk-ins will be welcome.

He said to support an anticipated increase in demand this weekend, more workers, more cubicles, more walk-up capacity and 60,000 more appointments will be available at key vaccination centres.

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Hours at major hubs including Bendigo, Sandown and La Trobe University in Melbourne have all been extended specifically for the blitz, which will run from this Friday to next Monday.

"This is a big push. Thousands of appointments are available, walk-in capacity has been expanded, opening hours have been extended, and more vaccinators will be on the floor," Mr Andrews said.

"If you got your second dose in October or earlier, now's the time to come along to one of our major state-run centres this weekend and get your third, to protect yourself and the community for the busy year ahead."

Walk-up vaccinations will be available and are encouraged at a number of state-run centres, including:

Visit coronavirus.vic.gov.au/vaccination-centres for locations, hours and access information before walking up.

Bookings can also be made online at portal.cvms.vic.gov.au or by calling 1800 675 398.

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Those who want to get their third dose at a local GPs or pharmacy can also book through the online clinic finder at covid-vaccine.healthdirect.gov.au/booking/.

For information about coronavirus visit coronavirus.vic.gov.au or call 1800 675 398.

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