Actuary and mathematics expert says his modelling shows there were about 20,000 carriers of COVID-19 in Australia in early April and not the 3000 active cases reported.
COVID-19 modelling completed for the Actuaries Institute suggests there were as many as 20,000 virus carriers in Australia at 9 April, far higher than 3000-plus active cases reported at the time.
The modelling also urges government and non-government working groups throughout the country to have a better understanding of the true spread of the disease, and the risks, before restrictions are relaxed.
In an article prepared for the Actuaries Institute's COVID-19 Working Group, Douglas Isles, an actuary with a Master of Arts in mathematics from Cambridge University, said modelling suggests that at 9 April there may have been around 20,000 carriers of COVID-19 in Australia, a much higher number than the 3000 or so active cases reported.
The modelling mirrors research by Dr Christian Bommer and Professor Sebastian Vollmer from Göttingen University in Germany. They used estimates of COVID-19 mortality and time until death, from a study published in The Lancet Infectious Diseases, to test the accuracy of official records and discovered, on average, that only about six per cent of coronavirus infections were being reported. The true number of infected people worldwide may have already reached several tens of millions, they estimated.
Mr Isles said a straightforward analysis of available data suggested that confirmed active cases in Australia are hugely under-reported.
“The focus in the media has been on three key data points around COVID-19: deaths, confirmed and active cases,” he said.
“We need to talk more about estimates and monitoring of community infection. Those risks need to be better understood before authorities decide when and how to relax current restrictions, an issue looming large for policymakers.
“Noting there are a lot more people with COVID-19 than there are confirmed cases, the public needs to be aware of the need for greater vigilance.”
Actuaries Institute chief executive Elayne Grace said the institute had established a working group to help advise its professional members, industry and policymakers seeking to understand the impact of the virus on our society and economy.
“We are looking at community health aspects, but also how the virus impacts business sectors as diverse as health, insurance and superannuation …
“The Actuaries Institute working group will also undertake assessments and approaches that can help governments and other groups manage Australia’s eventual end to this lockdown period and ensure the impacts are as limited as possible.”
Mr Isles said that while the modelling was simple, “the key point is that the reported data is an order of magnitude less than the actual data”.
He said his model was based on a number of authoritative sources including the Department of Health and the World Health Organisation (WHO).
Australian Department of Health data showed 330,000 people had been tested for COVID-19 at 9 April. At that time, there were 6103 confirmed cases, 51 deaths and 2987 recoveries.
The median age of death was 79, the median age of cases 47, and most cases were acquired overseas.
Mr Isles also used WHO data that tracked time lapses from the onset to recovery in various scenarios, including mild and severe cases. He said he used Australia-wide data covering 9 April statistics, plus rate of population testing, number of positive results and recovery and fatality rates.
He explained that using a constant carrier mortality rate and a constant time frame from infection to death allowed modellers to infer new carriers at a point in time. Applying a carrier mortality rate estimate of 0.5 per cent to the data on Australian COVID-19 deaths suggests there may have been around 400 new carriers per day in the week to 12 March, and 800 per day in the week to 19 March. This means it was likely that there were around 10,000 carriers by 19 March, and more than 20,000 carriers by 9 April.
“With access to more granular data, particularly around the demographics of those tested and the dynamics of viral transmission, these estimates could be improved,” he said.
“For COVID-19 we have a sample of 330,000 people tested, which is over one per cent of the population. It is reasonable for the public to expect to be provided with health experts' estimates of community infection rather than focusing purely on confirmed cases.”
The Actuaries Institute's COVID-19 Working Group involves a core group of 13 actuaries, supported by a further 50 actuaries working on a wide range of issues, advising business leaders, regulators and policymakers.
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