Although data suggest temperature and humidity may affect viral viability and transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), as SARS-CoV-2 is an emerging virus, the seasonality of coronavirus 2019 (COVID-19) cannot yet be definitively determined, according to a perspective article published in the Journal of Infectious Diseases.1
In this brief perspective article, the authors explored the question of the seasonality of SARS-CoV-2 by reviewing 4 lines of evidence related to viral viability, transmission, ecological patterns, and observed epidemiology of COVID-19 in the Southern Hemisphere’s summer and early fall.
Laboratory experiments have demonstrated that temperature and humidity affect the viability of coronavirus and influenza, and SARS-CoV-2 has been found to have similar stability under experimental conditions. Data may be emerging regarding SARS-CoV-2 viability in different environments within engineered aerosols and simulated body fluids, noted the authors. However, as laboratory experiments typically rely on engineered culture mediums, aerosols, or droplets, and/or rely on animal models, the findings may not generalize to clinical conditions.
Studies neither published nor peer reviewed have examined ecological associations between SARS-CoV-2 transmission patterns and climate. Findings from one study showed that prior to March 22, 2020, 90% of SARS-CoV-2 global transmissions occurred within areas with temperatures ranging from 3°C to 17°C and absolute humidity ranges between 4 and 9 g/m3 daily.2 Findings from another study showed that as little as a 1˚C increase in temperature and a 1% increase in relative humidity can lower the daily effective reproductive number by 0.0383 and 0.0224, respectively.3 However, the evidence is still developing and is somewhat inconsistent. In addition, travel and behavioral patterns potentially confound the relationship between environment and transmission. Human factors such as lack of sustainable social distancing and low immunity to a novel virus with high transmissibility will likely outweigh the climate effects on transmission.
Furthermore, rapid viral spread is not solely limited to areas within temperature ranges of 3°C to 17°C and humidity levels between 4 and 9 g/m3. For example, COVID-19 has been reported in countries lying entirely south of the equator including Argentina, Australia, Bolivia, Chile, Eswatini, French Polynesia, Mayotte, New Zealand, Namibia, Paraguay, Réunion, Rwanda, Seychelles, South Africa, Tanzania, Uruguay, and Zambia.
“Therefore, it seems unlikely that the coming Northern Hemisphere summer will have a significant effect on SARS-CoV-2 transmission reduction,” concluded the authors. “As to whether or not COVID-19 will enter into regular circulation like other human coronaviruses and influenza, this will depend largely on the duration of immunity to the virus, which remains unknown,” they added.
1. Kanzawa M, Spindler H, Anglemyer A, Rutherford GW. Will coronavirus disease 2019 become seasonal [published online June 21, 2020]? J Infect Dis. doi:10.1093/infdis/jiaa345
2. Bukhari Q, Jameel Y. Will coronavirus pandemic diminish by summer [published online March 17, 2020]? SSRN. doi:10.2139/ssrn.3556998
3. Wang J, Tang K, Feng K, et al. High temperature and high humidity reduce the transmission of COVID-19 [published online March 9, 2020]. SSRN. doi:10.2139/ssrn.3551767