While I don't know the specifics for Australia because I am not Australian, I can say that I've seen news articles that say "unnamed Biden officials have said the Axios report is a wake up call, because the Pfizer vaccine efficacy rate against the delta virus is 42%" in a population of 35,000 individuals, many of whom are over 60.

While the vaccine may prevent the severity of the illness, it is having a hard time preventing the spread of the illness.