'Silent' COVID-19 infections – cases in which individuals carried the virus without symptoms and avoided testing or isolation – likely exacerbated the pandemic's early spread and distorted containment strategies, a novel QUT behavioural economics study has found.
- Behavioural economics study shows not testing (and isolating) of asymptomatic people prolonged COVID-19 pandemic
- Fewer asymptomatic people sought COVID testing when perceived risk was low, while testing increased with heightened risk perception driven by reported case surges.
- This led to underestimates of infection and of 'excess deaths' when testing was symptom-based.
- Study advocates for incentivised population-level affordable, accessible rapid testing in future pandemics
Associate Professor Jayanta Sarkar, from QUT's School of Economics and Finance, said the study was one of the first to investigate the interaction between testing and isolation (T&I) behaviour and disease transmission, while most studies focused on behaviours to avoid exposure to the virus.
"Until now, T&I as a personal protective behavioural response and its implications for disease transmission and severity had not been analysed in the literature," Professor Sarkar said.
"This research integrates global data, showing estimates of the prevalence of asymptomatic COVID-19 varied from 1.2 to 91.9 per cent of all recorded infections and accounted for many 'excess deaths'.
"One study had found that excess deaths during 2020 and 2021 were 2.4 to 3.1 times higher than reported COVID-19 deaths.
"The model demonstrates how self-motivated testing choices create a self-reinforcing cycle.
"Early reliance on symptom-based testing inevitably missed many asymptomatic cases and underestimated the true level of community transmission.
"However, surging reported rates heightened risk perception, which spurred voluntary testing and isolation, even among the asymptomatic people.
"Higher T&I curbed the peak infection rate predicted by epidemiological models that ignored these behavioural adaptations and disregarded the prevalence-sensitive protective behaviour which skewed infection rate data that was critical for policymaking."
Professor Sarkar said later resurgences of COVID-19 infections reflected the fact that people were perceiving less disease risk as reported infection rates waned and restrictions were lifted.
"Thus, the same self-protective behaviour that helped curb infection spikes, also prevented a complete eradication. This also partly explains why we observed multiple waves and variants of the virus over a prolonged time.
Professor Sarkar said the study demonstrated the need for incentivising regular, accessible, rapid and accurate testing.
"My findings highlight the fact that undetected infections don't just distort infection prevalence and death estimates – they prolong outbreaks.
"The decision to test and the subsequent possibility of having to isolate to protect others from the disease entail a mental calculation of benefits and costs, such as loss of income or social interaction.
"Given that asymptomatic people do not feel sick and rely on outside signals to guess their infection risk, they are more likely to test and isolate when the existing infection prevalence is high.
"This two-way feedback between personal T&I behaviour and community infection rates has significant implications for the success of future disease management policy, because if we fail to detect asymptomatic carriers, we will definitely underestimate the true extent of community transmission.
"Undetected infections lead to an underestimation of the initial disease burden, while unattributed infections and deaths distort critical measures of disease severity which can influence the implementation of restrictive health policies like lockdowns," he said.
"A vast proportion of 'excess deaths' was directly attributable to undetected infections. Unattributed deaths contribute to an underestimation of excess mortality, with lower testing capacities exacerbating this issue.
"These results boost the calls for a robust global COVID-19 monitoring system and data sharing, potentially using worldwide flu surveillance infrastructure.
"Strategies to expand testing capacity under resource constraints, alongside targeted public awareness campaigns emphasising the benefits of early testing and isolation, could prevent thousands of deaths and reduce undetected transmission during critical phases of outbreaks."
The study, To test or not to test? A new behavioral epidemiology framework for COVID-19 was published in PLoS One.
