Modeling the effects of pandemics on physiology-related fertility decline in society.

Pandemics throughout history have raised challenges in many forms, such as increased mortality rates, economic instability, and political shifts. Recent pandemics, coupled with globally declining fertility rates, pose unprecedented demographic challenges for humanity. A pandemic is inherently connected to a population's fertility in many ways - psychological, economic, and, most importantly, physiological. Nevertheless, this connection is mostly left unintended, blinding us to the effects of the pandemic-caused physiological fertility decline on the population's growth over time. In this study, we proposed a novel epidemiological model incorporating physiological fertility decline dynamics using an extended Susceptible-Infected-Recovered (SIR) model incorporating age groups, genders, birth and death dynamics, and infection-induced physiological fertility decline. Our model, based on real-world data from 10 large cities globally, demonstrates the impact of infection on fertility, which can persist for generations, creating demographic ripple effects that extend well beyond the immediate pandemic period. That said, the fertility drop is secondary to the pandemic spread, even for relatively high fertility decline due to the pathogen. These results have significant implications for public health policy and population planning. They highlight the need to integrate fertility considerations into pandemic preparedness strategies. Our study provides a quantitative framework for assessing the long-term demographic impacts of pandemics, offering policymakers tools to assess and potentially mitigate the impact of future disease outbreaks at the population level.