Unseasonal respiratory syncytial virus epidemics during the COVID-19 pandemic: relationship between climatic factors and epidemic strain switching.

Abstract

Objectives: The coronavirus disease (COVID-19) pandemic affected respiratory syncytial virus (RSV) epidemic patterns. However, effects of climatic and virological factors on RSV epidemics remain poorly understood. We investigated the incidence of RSV infection in Okinawa, Japan; Taiwan, China; and Florida, USA before and after the COVID-19 pandemic, focusing on the effects of population mobility and climate.

Methods: We investigated correlations between RSV incidence, human mobility, and climate, pre- and post-pandemic. The second variable region of RSV G proteins was analysed phylogenetically using viral genomes isolated from patients in Okinawa with acute respiratory-tract infections.

Results: Annual RSV epidemics in Okinawa were not correlated with human mobility post-pandemic. The temperature and humidity zones at the RSV epidemic onset differed between pre- and post-pandemic periods; the respective standard deviations decreased. Genetic analysis of RSV strains from 2020 to 2022 revealed a cluster with low genetic diversity, markedly different from pre-2019 or 2023 prevalent strains.

Conclusions: Reduced human migration led to an RSV epidemic caused by an indigenous endemic strain, demonstrating the natural relationship between the epidemic and climatic factors. These findings could help develop effective prediction and control programs for RSV epidemics and inform the development of an effective vaccine program.