Coronavirus vaccines are seen as crucial to reviving an industry that saw worldwide passenger numbers fall 75.6% last year.
Chief executive Alan Joyce said many governments were talking about vaccination as "a condition of entry".
Even if they weren't, he thought the airline should enforce its own policy.
"We have a duty of care to our passengers and to our crew, to say that everybody in that aircraft needs to be safe," Mr Joyce said.
He believes that would justify changing the terms and conditions on which tickets are booked.