I don't think 80% works for most vaccines.
To provide protection for those who cannot
be vaccinated I have seen something like 95% being
quoted. This is for vaccines that provide actual
immunity and block transmission. These new
vaccines can't do that.
Also, you need to be careful comparing Australia
with Singapore. Australia has a very low population
density, even in Sydney, compared to Singapore
with one of the highest population densities in
the world.