If you want some references :

I’ll update this comment with a few :

1) Here is first one -

https://www.abs.gov.au/articles/population-change-2020

This one is 200k / 1% of total population lost in 2020 alone, 2021 would be much worse with much more restrictions and for past 10 months instead of 9 months

Extrapolated 2-3% is quite within margin of error.

1. Check covidlive by age group and lga’s

https://covidlive.com.au

a) 12-29 age groups, mostly the 16-29 has massive gaps ie 10-20% drops due to - mismatched census data ie students moving out of city and either back with parents, just further out of town and/or

b) Places like ACT with over 100%, again census data out dated

c) LGA’s like Yarra, Randwick, Inner west (Sydney), Sydney + Melbourne LGA’s on 77-80% as again census data out of date, people moving out of city etc

I’ve done the maths to account for population per age group and locality etc

1. Here is a research on the difference that is a bit complex but worth a look through

https://journals.sagepub.com/doi/full/10.1177/2378023121994014

So, as above.., I could add more but that should do for now - population net migration fell 1/4million for 2020, 2021 will be worse - so easily 2-3% is justified, I’d say likely even more is illustrated by first reference. Census data mismatch is articulated in 3) but the indicators in 2) of 10-20% in either heavily populated inner city lga’s and 16-29 age groups can be extrapolated to again another 1/4million to almost 1million, so again another 2-3% of the population, although some of it will be overlapping the internationals… what is left after 94% is vaxxed with another 1% being vaxxed within weeks is less than 1% - made up of anti-vaxxer and vaccine-hesitancy with a tiny fraction of people that have legitimate medical reasons…

That is about is as much as I have patience and time to go into… again not perfect numbers - so if you have something better - appreciate it.