The lockdowns in NZ and Vic were intended to eliminate the virus. That's why we didn't re-open until we'd had a series of double-donut days. Elimination was achieved by preventing onward transmission for a period of time at least as long as the lifecycle of the virus, which was in turn achieved by getting people to stay at home and minimise movement in the community.
The point is that what worked in Melbourne against the first variants of the virus didn't work against Delta because it was just too transmissible and we didn't see numbers fall the way that they did in lockdown 2.0. So, it became obvious that vaccination was the only way out, hence the big push on it. If this new variant is even more transmissible than Delta then lockdowns may not help much. In addition, the community has probably had it with lockdowns so compliance is likely to be an issue. So - masks and, if necessary, updated vaccines.
And if the Omnicron variant is more transmissible that will make it even less likely that the unvaccinated will avoid infection.

