COVID-19 is in a bit of a holding pattern at the moment.

It's not getting worse in Sydney, but then again despite lockdowns now going for several weeks it's not getting better yet either.

In Melbourne, it's still too early to know how the outbreak is trending, but case numbers have remained in the high teens over the weekend.

But we are learning more by the day about the Delta variant, and how it works in a low vaccination environment and under lockdowns.

So on today's Coronacast, the one number that helps contact tracers get cities out of lockdown.

Also on today's show:

* A clarification on the average number of contacts per COVID-19 case, and what happens under lockdowns

* Average ages of the Victorian outbreak

* What is happening to unused doses? Are they out there? We want to hear from you!