I feel I should point out that YOUR math is incorrect, as is your characterization of the tourist impact on herd immunity.
"7,4 million divided by 24 + 7,4 million equals 0,2356... => It is rather approximately 20% than 30%!"
This is incorrect. It's easy to check. The population of Australia isn't 31.4M. The tourists are an unknown, and cannot be added to the vaccinated population in order to derive herd immunity for the Australian population.
They aren't part of the herd.
Furthermore, while the tourists aren't long term residents, any diseases they bring with them, if communicated, will be. Since the total number of tourists, and the diseases they bring, does interact with the population of Australia, it is correct to consider that 7.4M tourists are impacting the herd, not some subset of them at any time.
After all, in an virulent epidemic, the early victims die, and the numbers of the population decrease, but this does not impact herd immunity, as their impact has already occurred, just as even temporary visitors' impact does.
@chron's a kid. You're supposedly a doctor with decades of training, and professional competence. His math was correct, and yours isn't. I reckon you owe him an apology. More than that, I think you should carefully examine your understanding of epidemiology, and vaccine safety.
You owe it to your patients, for sure, to not make such errors in their care.