Why Nose and Mouth Coverings are Highly Recommended to Impede SARS-Cov-2 Spread

In fourteen months the number of infected people with SARS-COV-2 has reached more than 159 millions and from those more than 3 million have resulted in death. There is now a consensus that the airborne saliva droplets, that are produced while speaking, coughingor sneezing by infected people is one of the most likely routes of transmission of the corona virus disease (COVID-19). The expelled droplets can measure between 0.4 and 450 μm in diameter. Once the droplets are in the air, they are subject to the gravitational, and air frictional forces that dictate their motion. Through exhaustive aerodynamic studies it has been shown that the aerosol droplets (less than 5 μm) can remain in the environment for very long periods of time and be transported by air currents. Larger droplets take shorter times and land within a circle of 1.5 to 2 m radius. Of key importance is the droplet size distribution and many efforts have been done to characterize this. By modeling the production of the number of saliva droplets with log-log Gaussian distributions, the virial load of the expelled droplets is estimated as a function of droplet size. Assuming a constant virus density, we estimate the amount of virus delivered into the environment. The use of face masks reduce drastically the amount of droplets emitted to the air by an infected person and to be inhaled by a healthy one. We emphasize the great importance of using adequate face protection to minimize COVID-19, transmission and to reduce the death toll due to this disease.