Virus can travel 20 feet, 6 ft inadequate: Study

Washington: Scientists have modelled the spread of infectious droplets from coughing, sneezing, and breathing under different atmospheric conditions, and found that the novel coronavirus can spread up to three times further in cold and humid weather.

According to the researchers, including those from the University of California Santa Barbara in the US, droplets carrying the virus can travel up to 20 feet, making the current social distancing norms of six feet insufficient to contain its spread.

Based on previous research, they said as many as 40,000 respiratory droplets can be generated by sneezing, coughing, and even normal talking, with initial speeds ranging from a few metres per second to more than a hundred meters per second.

From these past studies, the scientists said both the aerodynamics of the droplets, and their heat and mass exchange process with the environment can determine the effectiveness of virus propagation.

In the yet-to-be peer reviewed study, published as a preprint in medrXiv, the scientists used a comprehensive mathematical model to explore the evaporation, heat transfer, and projectile motion of respiratory droplets under different temperature, humidity, and ventilation conditions.

They found that the transmission pathway of COVID-19 through respiratory droplets is divided into short-range droplet contacts, and long-range aerosol exposure.

"While large droplets usually settle onto a surface within a limited distance due to gravity, smaller droplets evaporate rapidly to form aerosol particles that are able to carry the virus and float in air for hours," the scientists wrote in the study.

According to their analysis, the effect of weather conditions on this pathway is not the same every time. Low temperature and high humidity facilitates droplet contact transmission, while high temperature and low humidity promotes small aerosol-particle formation, the researchers said.

"Our model suggests that the 6 feet of social distance recommended by the Center for Disease Control and Prevention may be insufficient in certain environmental conditions, as the droplet spreading distance can be as long as 6 metres (19.7 feet) in cold and humid weather," the scientists wrote in the study.