In the midst of the coronavirus pandemic, two human factors are battling it out: Awareness of the virus’ severe consequences and fatigue from nine months of pandemic precautions, suggests a new study.

The results of that battle can be seen in the oddly shaped graphs of the cases, hospitalizations, and fatality-counts, says co-author Jonathan Dushoff, professor of biology and member of the Michael G. DeGroote Institute for Infectious Disease Research (IIDR) at McMaster University.

“This study underlines the importance of human behaviour in driving epidemic outcomes,” said Dushoff. “To make good predictions beyond the short term, we need to understand all of the factors driving human responses to the virus — fear, fatigue, information, misinformation, and so forth. We have a long way to go.” 

The tension between awareness and fatigue can lead to case-count plateaus, shoulder-like dynamics, and oscillations as rising numbers of deaths cause people to become more cautious before they let down their guard to engage once again in behaviours that increase risk for transmission. This, in turn, leads to rising death counts — and renewed awareness.

“Epidemics don’t necessarily have a single peak after which the risk subsides,” said co-author Joshua Weitz, professor of biological sciences at Georgia Institute of Technology. “People’s behaviours are both influenced by and influence epidemic dynamics, potentially driving plateaus, and oscillations in incidence.”

A paper describing the connection between human behaviour and viral spread was published this month in the journal Proceedings of the National Academy of Sciences. It was authored by researchers at Georgia Tech, McMaster University, Princeton University, and Texas A&M.

In the early days of the pandemic, many scientists turned to traditional epidemiological studies, which showed epidemic cases could rise to a peak and then fall smoothly as immunity to the infection reached high levels in a population in the absence of large-scale interventions. Public health messages urged the population to “flatten the curve” to prevent disease from overwhelming hospitals.

“We were concerned that a focus on ‘the peak’ was potentially misguided because it implied that the shape was a feature of the disease alone without considering the consequence of behaviour,” Weitz said. “In reality, there does not have to be a single peak during an epidemic.”

The research team analyzed data from the early phase of the epidemic and found evidence that the decrease in fatalities after a peak was slower than the rise toward it. However, in contrast to simple models of awareness-driven behaviour, the research team also found evidence that individuals tended to increase their activity — as measured by mobility indicators — before epidemic severity waned. This means that individuals may have grown fatigued, worsening the epidemic severity.

The study also found that other preventive measures, like mask wearing, have the potential to avert worst-case outcomes in disease transmission even as mobility increases in light of fatigue.

“If people are aware of the severity of the epidemic, they may change their behaviour, and if they change their behaviour, there will be fewer severe outcomes,” Weitz said. “But if awareness is short-term, individuals may tire of public health regulations and the virus will come roaring back. Instead of a single peak in cases, there can be plateaus or oscillations balanced between cautious behaviour and relaxation.”

Weitz and Dushoff share optimism as well as concerns on the potential effects of anticipation of imminent vaccine distribution on behaviour associated with transmission.

“It’s hard to be sure what impacts vaccine distribution will have on behaviour,” Dushoff said. “There is concern in public health circles that people who think the vaccine is just around the corner could relax their guard. Human behaviour is complicated.”

Lessons for future public health responses may help focus on the role of human behaviour as well as communications that make disease impacts personal, fostering long-term awareness and changes in behaviour that can reduce collective transmission.

Weitz and Dushoff coauthored the study with Sang Woo Park of Princeton University and Ceyhun Eksin of Texas A&M.

The research was supported by the Simons Foundation, the Army Research Office, National Institutes of Health, and National Science Foundation.