Victoria’s skyrocketing case numbers are finally starting to flatten as the effect of mandatory mask rules start to play out, says one expert who said there was a good reason for this week’s “rollercoaster” of numbers.

Deputy Chief Health Officer Allen Cheng said that while Victorian authorities did not have certainty around when numbers would peak, they “can’t find anything that looks like” 1100 cases a day.
In fact, the curve of Victoria’s numbers may instead be flattening, University of Melbourne Professorial Fellow in Epidemiology Tony Blakely said in an interview.
While case numbers had been “a rollercoaster” of wide of variation in the last week, he said this was because of the “batching” of testing swabs.
By this, he meant tests were reported in big data sets to the DHHS or large batches of swabs were sent to labs in one go.
There were 471 new cases reported on Thursday, after a record-breaking 725 on Wednesday. This was preceded by two days of case numbers around 400 after a jump of 671 new cases on Sunday.
“What this [batching] means in practice is that the daily numbers are up and down by more than chance variation in the true infection rate per day, Professor Blakely said.
“But when you smooth those cases to a five day average, giving the most weight to the day in the middle, it looks a lot less alarming.
“With that smoothing, it looks like there was a kink on July 30. You could say that’s just a bump in the data, but we were wearing masks in the seven days leading up to then so the kink makes sense.”
Melbourne’s mandatory mask rules came into effect at midnight on July 22.
While the case curve was still bent, Professor Blakely it was starting to “look flattish now”.
“At the macro level, which is as much as we can do, it certainly looks like there’s been a turn. Predicting the future is always risky, but you’d strongly expect that curve to take another bend in 10 or so days when stage four takes effect.”
Dean of Health Sciences at Swinburne University Bruce Thompson said the batching meant that the virus’ reproduction rate, rather than new cases, was the more telling measure of how case growth was tracking.
“They do this in batches and release information in batches, so this number is going to bounce all around like a pinball ball,” Professor Thompson said.
“The number that is then more important now is the reproduction number, meaning how many people do I give the virus to. Do I give it to no one because I’ve isolated, or do I give it to other people?
“In stage three, it was sitting at about 1.8 and we got it down to 1.3, but everyone was still giving it to people. Now in ten days [after two weeks of stage four] we want to see it down below one, and then maintain that for a few weeks.
“That will let us get numbers dropping to lower levels consistently. And from what I’m seeing now, when there’s noone around the streets, yet it will come down because people aren’t seeing each other.”
Professor Blakely said that when new cases were consistently at or under 200 a day, better contact tracing would then help stem new infections.
“[That level] will enable our contact tracing teams to get back into a zone where they can be more effective and not overwhelmed.”