The paradox of rapid and synchronized propagation of seasonal influenza ‘A’ outbreaks in contrast with COVID-19: a testable hypothesis

Seasonal influenza A virus (SIAV) apparently exhibits a paradoxical pattern: despite a lower basic reproduction number (R₀) than SARS-CoV-2, it propagates across the Northern Hemisphere with remarkable speed and synchronicity. We propose a testable hypothesis, developed in two conceptual steps to explain this phenomenon. First, we discuss what may explain the rapid, near-synchronous propagation of SIAV seasonal outbreak. We suggest that it may result from parallel seeding from multiple sources, rather than emerging from a singular origin, as observed with COVID-19. Second, we examined potential mechanisms for parallel seeding. We propose a hypothesis-generating framework that, despite its limitations, offers a structured approach for integrating avian ecology with human epidemiology. The hypothesis is testable through genomic and metagenomic methods. Sequencing viruses from humans and migratory birds across regions may be evaluated to reveal identical viral lineages. The hypothesis may highlight the potential role of ecological reservoirs in global influenza propagation dynamics. If validated, this framework would advance understanding of influenza seasonality and may guide integrated surveillance strategies linking avian ecology with human epidemiology.