Roles of humidity and temperature in shaping influenza seasonality

Abstract

Experimental studies in guinea pigs demonstrated that influenza virus transmission is strongly modulated by temperature and humidity. A number of epidemiological studies have followed up on these findings and revealed robust associations between influenza incidence in temperate regions and local conditions of humidity and temperature, offering a long-awaited explanation for the wintertime seasonality of influenza in these locales. Despite recent progress, important questions remain as to the mechanism(s) by which humidity and/or temperature affects transmission.

FIG 1

The efficiency of respiratory droplet transmission in guinea pigs varies with humidity and temperature. Transmission efficiency, calculated as the percentage of exposed guinea pigs that contracted infection, is plotted against relative humidity (A) and absolute humidity (B). In each case, data points obtained at 5°C are blue, those obtained at 20°C are yellow, and those obtained at 30°C are red. Numbers within or adjacent to the symbols indicate the number of replicate experiments represented. Trend lines shown in panel A were drawn freehand. Data are reported in references , , and , with the exception of the results of the experiment at 5°C and 20% RH, which is unpublished. The data shown include results obtained with both the A/Panama/2007/1999 (H3N2) and A/Netherlands/602/2009 (H1N1) viruses.