The vaccine push follows the Victorian government's decision this week to slash the interval between the second and third doses for adults from four months down to three months with immediate effect.

The shift in vaccine policy, which aligns with ATAGI advice, was made with a view to relieving the crippling impact of the Omicron wave on the state's hospital system and comes after a state-wide code brown emergency was declared.

In Victoria, around half the people hospitalised with the Omicron variant are unvaccinated, while over 45 per cent are double vaccinated.

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The findings of several leading studies show that a third dose of an mRNA vaccine is essential to restoring immunity and protection against Omicron infection in people more than three months post their second dose.

Emergency doctor Mark Harris, who serves as a Ballarat councillor, said accelerating the booster program would reduce pressure on the health system as well as the wider community.

"The sooner we get the booster the better because it protects not just you and the heath system, but the economy as well," Dr Harris said.

"We've got supply chains breaking down in many places; there's no part of the economy that isn't essential, so just get your booster - I couldn't be more blunt."

From 8.30am on Sunday, the vaccination clinic at The Mercure will accept a limited number of walk-in appointments for 18-year-olds and over for Pfizer boosters, with walk-ins to stop once capacity is reached.

On Friday, walk-in capacity was exhausted by 9.30am, suggesting community demand for boosters was high.

In addition to the Super Sunday blitz, limited walk-ins for boosters will also be accepted this Saturday and Monday 9am-3pm.

BHS had temporarily suspended walk-ins to cope with the demand created by the rollout of the paediatric vaccine for children aged five to 11 years.

Grampians Public Health Unit vaccination operations director Lisa Oro said BHS would "continue to review availability for walk-ins and offer them when possible".

"Ballarat Health Services would like to thank those who have rolled up their sleeve to help protect our community and also our staff who are playing an important role during these challenging times," Ms Oro said.

Vaccine bookings can be made online at http://portal.cvms.vic.gov.au or by calling 1800 675 398. Note bookings are essential for the children aged five to 11 years.