Seasonal Shifts in Influenza, Respiratory Syncytial Virus, and Other Respiratory Viruses After the COVID-19 Pandemic: An Eight-Year Retrospective Study in Jalisco, Mexico

Abstract

The coronavirus disease 2019 (COVID-19) pandemic profoundly disrupted respiratory virus epidemiology through widespread non-pharmaceutical interventions (NPIs), such as mask-wearing and social distancing. This retrospective study explores the seasonal patterns and incidence of influenza virus, respiratory syncytial virus (RSV), and other respiratory viruses over an eight-year period in Jalisco, Mexico, to understand shifts in virus circulation across the prepandemic, pandemic, and postpandemic phases. Weekly case counts were analyzed using an interrupted time series (ITS) model, segmenting the timeline into these three distinct phases. The ITS results revealed abrupt reductions in viral incidence during the pandemic, followed by notable resurgences as NPIs were relaxed. Influenza A (H3) predominated in 2022, while influenza B surged in 2023, and Influenza A H1N1 cases increased subsequently. RSV exhibited an earlier onset and heightened activity compared to prepandemic trends. Other viruses, including human enterovirus/rhinovirus and human parainfluenza virus, showed altered patterns, with some failing to return to prepandemic seasonality. These findings highlight the complex interplay between viral ecology and population immunity, influenced by pandemic-related behavioral shifts. The results underscore the need for adaptive surveillance systems and targeted vaccination strategies to address evolving respiratory pathogen dynamics and mitigate future public health impacts.