I did some back of the fag packet calculations earlier and even if every resident in Australia is vaccinated (which is a long shot), that still would leave around a million vaccinated inhabitants that are unlikely to have developed immunity, based on the published efficacy rates for western vaccines that are being used so far.
With no vaccine ever being 100% effective along with the current zero tolerance towards the virus at a government level, I struggle to see the border ever opening freely ever again unless there is a change in tactics from the government.