The Influenza-like Evolutionary Path of Respiratory RNA Viruses

This study proposes a structural theory to explain the convergent evolution of respiratory RNA viruses toward influenza-like endemicity. We introduce the SIRS-G model, which integrates adaptive immunity A(t), antigenic drift V (t), and a dynamic immunity gap G(t) = |A(t) − V (t)|, with transmission governed by a nonlinear function β(G). To characterize evolutionary constraints, we construct the TEV Trian- gle, a framework modeling trade-offs among transmission, virulence, and immune escape. To support predictive governance, we propose the G-index as a threshold-based metric for anticipating reinfection waves. Together, these models explain why diverse viruses—despite differing origins—evolve toward mild symptoms, upper respiratory tropism, high transmissibility, and periodic resurgence. By integrating evo- lutionary virology, immune dynamics, and adaptive governance, this framework offers a unified system for modeling long-term viral behavior and informing public health strategy under structural uncertainty.