Model Shows COVID-19 Will Be Endemic, Sticking Around Like the Flu and Common Cold

“Herd immunity” is a fragile and transitory state

Spring 2022

Ateam of scientists, including Grainger Engineers, has developed an epidemiological model that encompasses the randomness and dynamic variability of individual social interactions, as well as individual differences in the size of social networks. It provides researchers and public health experts with a better understanding of COVID-19 and better tools to forecast future outbreaks in this pandemic and future epidemics.

The new model, which was detailed in the Proceedings of the National Academy of Sciences and eLife in 2021, was validated against empirical data taken from four US regions prior to the introduction of COVID-19 vaccines. The model tells us that COVID-19 may be here to stay — it shows a clear path for it to become endemic in the global population, much like the common cold or the flu.

Scientists at DOE’s Brookhaven National Laboratory, the University of California San Diego, and the University of Illinois Urbana-Champaign developed a stochastic social activity (SSA) model, which they paired to a traditional epidemiological model. The SSA is inspired by real-world observations based on proximity data, like the fact that any given individual’s social activity tends to happen in bursts over short time scales, with longer in-between periods reverting to average sustained social-activity levels.

The new SSA model builds on the researchers’ prior work that showed the concept of “herd immunity” does not apply to the COVID-19 pandemic, because this type of collective immunity to the disease turns out to be short-lived. Instead, what emerges is a fragile and temporary state of collective immunity, which they coined “transient collective immunity.” This earlier work captured individual heterogeneity of both biological and individual social-activity levels in one parameter they called the “immunity factor.”

Professor Sergei Maslov, a Bliss Faculty Scholar in the Bioengineering and Physics Departments, said the team’s work shows the endemic state is virtually guaranteed for COVID-19.

“I will be very surprised if it doesn’t stay with us for the future. This current study continues the social-network tradition of our prior work and fleshes out an idea we introduced at the end of that paper. Social activity levels are not just different for different people, but different for each person as a function of time.”