Susceptible host dynamics explain pathogen resilience to perturbations.

Abstract

Interventions to slow the spread of SARS-CoV-2 significantly disrupted the transmission of other pathogens. As interventions lifted, whether and when human pathogens would eventually return to their pre-pandemic dynamics remains to be answered. Here, we present a framework for estimating pathogen resilience based on how fast epidemic patterns return to their pre-pandemic dynamics. By analyzing time series data from Hong Kong, Canada, Korea, and the US, we quantify the resilience of common respiratory pathogens and further predict when each pathogen will eventually return to its pre-pandemic dynamics. Our predictions are able to distinguish which pathogens should have returned already, and deviations from these predictions reveal long-term impacts of pandemic perturbations. We find a faster rate of susceptible replenishment underlies pathogen resilience and sensitivity to both large and small perturbations. Overall, our analysis highlights the persistent nature of common respiratory pathogens compared to vaccine-preventable infections, such as measles.

Significance statement: COVID-19 interventions slowed the transmission of other respiratory pathogens, raising questions about the mechanisms driving differences in responses to COVID-19 intervention measures. To address this gap, we characterized pathogen resilience to perturbations by quantifying how fast each pathogen returned to its pre-pandemic epidemic cycles. We applied the resulting framework to data from Hong Kong, Canada, Korea, and the US, and showed that common respiratory pathogens are much more resilient than measles, a vaccine-preventable infection. Finally, we showed that the speed of replenishment of the susceptible population-for example, through waning immunity-largely determines a pathogen's resilience to perturbations, including large interventions and small stochastic changes in the dynamics.