COVID case numbers may be six times higher than reported

Embargoed until: Publicly released:
Peer-reviewed: This work was reviewed and scrutinised by relevant independent experts.

Simulation/modelling: This type of study uses a computer simulation or mathematical model to predict an outcome. The original values put into the model may have come from real-world measurements (eg: past spread of a disease used to model its future spread).

Australian researchers say the true number of infections in the COVID-19 pandemic could be around six times greater than the reported number of cases. The researchers used the number of reported deaths in 15 developed countries, including Australia, to look back and estimate the total number of people likely to have been infected to result in that death rate. In their analysis, Australia was the only country to have experienced a decline in the detection rate for COVID-19, with tests likely detecting around 50 per cent of infections in April, May and early June, but only picking up 21 per cent by the end of August. The authors say this decline is consistent with evidence that a resurgence of COVID-19 was accompanied by hidden transmission within communities by persons who were reluctant to get tested, even if sick, possibly because of the loss of earnings associated with self-isolation.

Journal/conference: Royal Society Open Science

Link to research (DOI): 10.1098/rsos.200909

Organisation/s: The Australian National University, The University of Melbourne, Ikigai Research, Tasmania

Funder: The authors received no funding for this study.

Media release

From: The Australian National University

Global COVID infection rates up to six times higher than reported

COVID-19 infection rates in the UK, France, Belgium and Italy are much higher than reported and in the case of Italy up to 17-times higher, new data shows.

Analysis also shows Australia had the best level of detection among the 15 countries at the end of April but the rate of infection may still have been be five times higher than what has been officially reported at the end of August.

In a paper published in Royal Society Open Science, researchers from Ikigai Research, The Australian National University (ANU) and the University of Melbourne show infection rates between March and August across 15 countries were on average 6.2 times greater than reported cases.

Study co-author Professor Quentin Grafton, from ANU, said the study estimated the true number of infections across a combined population of over 800 million people in 11 European countries, as well as Australia, Canada, South Korea and the USA.

“We found COVID-19 infections are much higher than confirmed cases across many countries, and this has important implications for both control and the probability of infection,” Professor Grafton said.

“For example, our analysis has found more than 5.4 million in the UK, 8 per cent of the population, are or have been infected with the coronavirus.

“In Australia, our modelling shows the actual rate (infected and recovered) at the end of August, may have been five times higher than reported, with 0.48 per cent of the population, or up to 130,000 people may have been infected. That’s much higher than the confirmed proportion of 0.10 per cent of the population.

“These findings raise serious questions about how we deal with all facets of the coronavirus pandemic, including ongoing morbidity and life-long health impacts for people who have been infected, how we implement and manage lockdowns, and how we make sure we are on top of this pandemic more broadly.”

The analysis used “backcasting”, a process that examines COVID-19 related fatalities and compares this with the time from infection to symptoms and time from symptoms to death. The authors state this method allows them to provide a 95 per cent confidence interval around their estimated true (population) infection rate.

“Simply put, we analysed statistics on how many people had died from COVID-I9 in a given country and then worked backwards to see how many people would have to have been infected to arrive at that number of deaths,” Dr Steven Phipps from Ikigai Research said.

“Our method is a novel and easy-to-use method for estimating the true infection rate wherever there is reliable data on the number of fatalities attributable to COVID-19.”

Professor Grafton said: “Our approach is particularly advantageous in locations where there is little testing or limited capacity to forecast rates of infection but where there is a need, for the purposes of public health planning, for a population measure of COVID-19 infection.”

The research is published by Royal Society Open Science.


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