WA’s Omicron wave on a downward trajectory, despite new variants

Sophisticated modelling produced by Telethon Kids Institute and Curtin University is predicting a steady decline in COVID-19 cases in WA throughout August, but hospitalisation rates will remain relatively high.

It is expected WA’s daily case numbers will remain around 5,000 for several more weeks, before dropping to around 3,000 a day at the end of August. Using a “big-data” software tool, the research team has been able to model the spread of the virus using the state’s unique physical and social geography, creating the most detailed COVID-19 modelling ever applied to an Australian outbreak.

The model creates a simulation of Western Australia’s 2.7 million residents, factoring in households, communities, schools and workplaces, with locations matched one-to-one against the real world in a way the researchers believe captures real interactions of our daily lives.

WA’s Omicron outbreak experienced a late-winter bump in numbers after the May peak, caused by the emergence of the BA4 and BA5 variants, but the new variants are not predicted to trigger a “second Omicron wave” as had been feared.

“If no new variants emerge in the short-term, we can expect WA’s Omicron wave to continue to tail off throughout August and into September,” lead researcher, Associate Professor Ewan Cameron said.

The emergence of the new sub-variants has made the winter Omicron wave last for longer right across Australia.

The case-to-hospitalisation ratio in WA is relatively high compared with other states, meaning there are more people in hospital with COVID than would be expected from the daily case numbers. Associate Professor Cameron said it is likely a range of factors has contributed to the recent surge.

“There are signs that older age groups in particular are experiencing elevated rates of transmission relative to the May peak” he said. “Despite a high coverage of third dose vaccination, uptake of the fourth dose is below 65% and acquired immunity from past exposure in this cohort is likely only modest.

“The admissions data confirm that more older people are making up the hospitalised in the later part of the outbreak.  The return of winter flu transmission to pre-pandemic levels may well be playing a role too.”

The first peak of this wave (May 18^th) saw 327 people in hospital, 45% of those patients were over 60. The second peak (July 21^st) saw 459 people in hospital, and 60% of those patients were over 60.

Associate Professor Cameron said the discrepancies between case numbers and hospitalisations could also indicate under-detection or under-reporting of cases, but there was no clear data to support that. 

He said international data did not suggest the BA4 or BA5 variants are more severe than other Omicron variants.