SARS-CoV-2 survives better at low temperatures and extreme relative humidity!

 Souradip Mallick, National Institute of Technology, Rourkela

For transmission of viruses from one host to the next, virions must remain viable(infectious) in the period between release from the transmitting host and uptake by the recipient host. Thus environmental stability like ambient temperature and humidity of viruses determines the potential for fomite transmission and for mid-to-long range transmission through the air. The novel zoonotic coronavirus SARS-CoV-2—the causative agent of the COVID-19 also varies in its environmental stability as a function of temperature and humidity, but the joint effect is still not clear. It is known that SARS-CoV-2 survives better at low temperatures and extreme relative humidities; median estimated that virus half-life was more than 24 hours at 10°C and 40% RH, but approximately an hour and a half at 27°C and 65% RH.

Thus the environmental stability of SARS-CoV-2 virions was observed in a suspended cell culture medium deposited onto a polypropylene plastic surface at nine environmental conditions: three relative humidities(RH; 40%, 65%, and 85%) at each of three temperatures(10°C, 22°C, and 27°C) and then the mechanistic biochemical model of virus decay kinetics was created. Also mathematical modelling, and a meta-analysis of existing literature, a mechanistic framework to quantify the joint effects of temperature and humidity on virus stability was developed which explains the SARS-CoV-2 stability on the environmental temperature and relative humidity.

Minimal virus decay occurred during the evaporation phase when excess water was present. Estimated half-lives were long but exact values were highly uncertain, as the small amount of absolute virus inactivation during the brief evaporation phases. Thus virus decay became markedly faster as temperature increased across all humidities, with decay at 27°C roughly five to ten times faster than decay at 10°C. Across temperatures, virus decay exhibited a U-shaped dependence on RH which is roughly two to five times faster at 65% RH than at 40% and 100% RH.

When released from infected hosts, virions are found in host body fluids, viral inactivation experiments are typically conducted in cell culture medium containing amino-acids and electrolytes i.e. sodium chloride (NaCl). It is obvious that higher quasi-equilibrium solute concentrations are associated with faster virus inactivation rates. Thus the ambient humidity greatly affects the reaction rate by setting the quasi-equilibrium concentrations of the reactants which induce inactivation of the virus.

By encoding the underlying chemistry into a mathematical model and estimating parameters using modern computational techniques, a probable relation was established. Also, it was observed that transmission risks are associated with cold and climate-controlled indoor settings, where as hotter, more concentrated solutions are unfavourable to viruses.

Also read: BIOLOGICAL AGE AND ITS MANIPULATION!

[REFERENCE]-  Dylan H. Morris, Kwe Claude Yinda, Amandine Gamble, Fernando W. Rossine, Qishen Huang, Trenton Bushmaker, Robert J. Fischer, M. Jeremiah Matson, Neeltje van Doremalen,  Peter J. Vikesland, Linsey C. Marr, Vincent J. Munster, James O. Lloyd-Smith; The effect of temperature and humidity on the stability of SARS-CoV-2 and other enveloped viruses; https://doi.org/10.1101/2020.10.16.341883

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