The Victorian government wants all Year 12 students to be vaccinated against coronavirus before exams in October, but hasn't explained how this will be achieved.
Education Minister James Merlino says the government has made it a "priority" to have all Year 12 students vaccinated before they start exams on October 4 - less than six weeks away.
He said there would be "very strong communication" to students, staff and the wider community to make it happen.
However, the timing is tight, with second Pfizer doses currently being administered up to six weeks after the first. The recommended gap between AstraZeneca doses is 12 weeks.
Mr Merlino would not say whether students would be able to get their second Pfizer dose in three weeks, or if they would be prioritised at the state's vaccination hubs.
"I'm not making any announcements today," he told reporters on Wednesday.
"This is about sending a very strong message to year 12 students, particularly in their final months, giving them confidence and clarity that they can really tackle the last few months of study and give it their best shot."
Mr Merlino also said the state remained hopeful children aged 12 and up could get their first dose of a vaccine by the end of the year, subject to health advice.
It comes as Victoria recorded 45 new locally acquired COVID-19 cases and the state government's vaccination website crashed as thousands of young people try to secure a booking.
Of the cases, 36 are linked to known outbreaks, while the source of the remaining nine infections are under investigation.
Twenty-eight cases were not isolating and infectious in the community.
The total number of active cases in the state is 538.
Health Minister Martin Foley said authorities still had "a lot of work to do" to bring the outbreak under control.
More than 830,000 vaccination bookings over the next four weeks opened from 7am on Wednesday for Victorians aged between 16 and 39, including 450,000 first-dose Pfizer appointments.
Within minutes of bookings opening, the website buckled due to high traffic.
Many people reported receiving a "500 internal server error" after waiting for up to an hour in the queue to schedule an appointment. Others made it through the queue, only to be told they were ineligible for the Pfizer vaccine.
The health department's COVID-19 response deputy secretary Naomi Bromley said the site received 50,000 hits per minute on Wednesday morning, while 1.3 million people had tried to call the coronavirus vaccination booking line.
"It is slow. It is busy. Please be patient. Please be kind to our staff," she said.
Ms Bromely said more appointments would be made available in coming days.
Opposition health spokeswoman Georgie Crozier said Victorians should be able to book with confidence.
"The Andrews Labor government has had months to get prepared and yet the confusion continues and the system crashes again," she said in a statement to AAP.
People aged 18 to 39 who have already made a first dose AstraZeneca appointment will be given the option to instead receive the Pfizer jab, while those aged 16 and 17 will strictly receive the latter.
People aged 60 and over will continue to receive AstraZeneca.
The expansion of the state's vaccine rollout is possible because of an additional 175,000 Pfizer doses the Commonwealth government imported from Poland.
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