Impact of short-term weather variability on influenza incidence under climate change

Influenza incidence has been proven to be closely associated with low temperatures. However, the role of temperature fluctuations in affecting influenza incidence is less quantified, especially in the context of global warming. This study constructed a short-term weather variability index (SWVI) to measure the cumulative fluctuations of minimum temperature between 2 consecutive weeks and comprehensively analyzed the impact of SWVI on current and future risks of influenza incidence in the mid-latitude region of Hubei Province, China. Influenza-like illnesses (ILI) data (2009-2020), meteorological observation data from 76 national stations (1979-2020), 10 global climate models in the Coupled Model Intercomparison Project Phase 6 (CMIP6) and distributed lag nonlinear modeling were used for analysis. The results showed that (1) the intra-annual variation of SWVI and the percentage of ILI (ILI%) in Hubei exhibited similar bimodal structures. A more significant correlation was detected between SWVI and ILI% than with sustained low temperatures, suggesting that SWVI may serve as a stimulus for influenza incidence. (2) From winter to spring, the response of relative risk (RR) of ILI% to SWVI was faster and greater than to low temperature. The most significant impact of SWVI on influenza incidence was observed at a short-term lag of 0 wk, with the highest increase in RR of ILI% recorded at 84.1% (95% confidence interval [CI]: 25.7-169.6%) for each 1°C increase in SWVI. In age-stratified analysis, younger people were more susceptible to weather variability than the elderly. (3) In the past 40 yr, the annual SWVI increased consistently, particularly in central and eastern Hubei. CMIP6 projections showed that SWVI would continue to increase with a stronger amplitude under scenarios of higher emissions. The risk of influenza incidence caused by short-term weather variability will inevitably increase, with the greatest risk anticipated at the end of the 21st century (76.4%).