Global warming drives the evolutionary rate of H1N1 and H3N2 influenza viruses

The H1N1 and H3N2 subtypes of the seasonal influenza A virus have circulated among humans for decades. Because of their pathogenicity, these viruses have been extensively studied from epidemiological, molecular and evolutionary perspectives. Their seasonality is primarily driven by variations in temperature and humidity, which also play a key role in shaping outbreak dynamics. Yet, despite numerous studies estimating the substitution rates of different Influenza A subtypes, it remains unclear whether these rates change over time in response to shifting climate conditions. To address this outstanding question, we collected genomic sequences of the hemagglutinin and neuraminidase genes for both H1N1 and H3N2 subtypes circulating worldwide. Keeping only sequences from countries with records spanning at least 2 decades, we performed a Bayesian analysis to estimate substitution rates. We show that substitution rate is driven by temperature for both subtypes and genes for multiple countries (Australia, China, Japan, Netherland, Russia, Thailand, U.S.A.). When it is not the case, a power analysis indicates a potential lack of sequences to detect the effect. As temperatures keep increasing due to global warming, further research is needed to understand if a speed up in the influenza evolution rate has any impact on epidemic burden.