Summary: A new mathematical model incorporates fear, both of infection and vaccination, to better understand how pandemics occur in multiple waves of infection, as we are witnessing with COVID-19.

Source: NYU

A new mathematical model for predicting infectious disease outbreaks incorporates fear — both of disease and of vaccines — to better understand how pandemics can occur in multiple waves of infections, like those we are seeing with COVID-19.

The “Triple Contagion” model of disease and fears, developed by researchers at NYU School of Global Public Health, is published in the Journal of The Royal Society Interface.

Human behaviors like social distancing (which suppresses spread) and vaccine refusal (which promotes it) have shaped the dynamics of epidemics for centuries. Yet, traditional epidemic models have overwhelmingly ignored human behavior and the fears that drive it.

“Emotions like fear can override rational behavior and prompt unconstructive behavioral change,” said Joshua Epstein, professor of epidemiology at NYU School of Global Public Health, founding director of the NYU Agent-Based Modeling Laboratory, and the study’s lead author. “Fear of a contagious disease can shift how susceptible individuals behave; they may take action to protect themselves, but abandon those actions prematurely as fear decays.”

For instance, the fear of catching a virus like SARS-CoV-2 can cause healthy people to self-isolate at home or wear masks, suppressing spread. But, because spread is reduced, the fear can evaporate — leading people to stop isolating or wearing masks too early, when there are still many infected people circulating. This pours fuel — in the form of susceptible people — onto the embers, and a new wave explodes.

Likewise, fear of COVID-19 has motivated millions of people to get vaccinated. But as vaccines suppress spread and with it the fear of disease, people may fear the vaccine more than they do the infection and forego vaccination, again producing disease resurgence.

For the first time, the “Triple Contagion” model couples these psychological dynamics to the disease dynamics, uncovering new behavioral mechanisms for pandemic persistence and successive waves of infection.

“If fear of COVID-19 exceeds fear of the vaccine, it may spur vaccination and therefore suppress the virus, a trend we saw in the U.S. this spring as millions of Americans were vaccinated and cases dropped,” said Epstein.

“But if people think the vaccine is scarier than the disease — whether they are skeptical about how serious COVID-19 is or because of baseless fears of the vaccine fueled by misinformation — our model shows that people avoid vaccines and a new disease cycle can grow. We’re seeing this play out in real time in regions with lower rates of vaccination, where the Delta variant is rapidly spreading and cases are surging,” added Epstein.

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