COVID-19 control measures in the Australian state of Victoria reduced the reproduction ratio of the virus from 1.75 to 1.16 and averted as many as 37,000 infections during July, according to a new study in the Medical Journal of Australia.
The research has not been peer reviewed but is available as a pre-print paper.
A team from the Burnet Institute, Monash University and the Peter Doherty Institute for Infection and Immunity examined daily diagnosed cases (excluding travellers in quarantine) as reported by the Victorian Department of Health and Human Services to estimate infection growth rates before and after the introduction of Stage 3 restrictions in 10 postcodes in the city of Melbourne on 1 July.
“We expected to see a time lag between the intervention being introduced and detecting its effect due to both the generation interval for the infection (estimated as four days), and delays in testing and reporting (estimated as three days). Hence, we regarded 14 June to 7 July inclusive as the pre-intervention period,” the authors write.
“We assumed that the initial growth rates would have continued, unchanged by the Stage 3 restrictions, until the cases reported on the 7 July 2020. We then measured the impact of the Stage 3 restrictions from 10 July, and thus the post-intervention period was from the 10 July to present (30 July 2020).
“The model projected 27,000 cases would occur from 1 July to 30 July if the growth rate had continued unchanged (R0 1.75), as opposed to the 8314 cases diagnosed in Victoria during this period.”
“The control measures introduced in Victoria from 1 July reduced the transmission of COVID-19, averting 9000-37 000 infections between 2 and 30 July,” they conclude.
Despite this reduction, there remains significant ongoing growth, with an estimated further 14% reduction in transmission required to control the epidemic, they write.
Stage 4 restrictions for metropolitan Melbourne were introduced on 2 August.