It is known that respiratory viral diseases emerge in seasonal cycles. Common colds and influenza are considered annual epidemics that affect many during the winter. Newly emerging viral epidemics likethe severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are also common during these months. 

Research suggests that environmental temperature and humidity significantly impact respiratory virus stability and transmission rates. Additionally, these factors modulate the host’s intrinsic, innate, and adaptive immune responses to viral infections in the respiratory tract.

Therefore, outdoor and indoor climates correlate to the seasonality of viral respiratory infections. Although cold and influenza infections show greater transmission rates during winter, other respiratory viral infections tend to peak during spring or summer. Other factors that influence viral transmissibility amongst hosts are – temperature, lighting, and humidity. Further research is warranted to unravel the mechanisms of spring-to-summer epidemics. 

Source: Annual Review of Virology. 2020 Sep 29;7(1):83-101. doi: 10.1146/annurev-virology-012420-022445