The modes of transmission of SARS-CoV-2 and other respiratory viruses: What we know now, and how to protect ourselves

The modes of transmission of COVID-19 have been the subject of intense controversy. Overwhelming evidence now supports that COVID-19 transmission is airborne: some infected people (those with high viral load) exhale espiratory aerosols, little balls of respiratory fluid or saliva that contain the virus, float in the air like an invisible smoke, and follow air currents. Aerosols infect when we inhale them, and easily explain substantial transmission in close proximity, superspreading events, less frequent long-distance transmission and why transmission indoors is far larger than outdoors. Surface transmission is difficult, and not a single case of surface transmission has been demonstrated. A small fraction of transmission may go through ballistic “WHO” droplets, mostly important when an infected person coughs or sneezes on someone else's face. “Droplet transmission” is mostly a historical error, confusing the real effect of dilution with a mostly imagined effect of gravity. The roots of the extreme resistance from WHO, CDC (and other Public Health authorities) to airborne transmission are rooted in a century of denial of (till 1962) and resistance (afterwards) to airborne transmission, since American public health luminary Charles V. Chapin in 1910 successfully changed the previous paradigm.

 

I will present some ideas about how to protect ourselves better from COVID-19 and other respiratory diseases, focusing on the ones that appear to be underappreciated: (1) the use of visible CO2 monitors in all public spaces where we share air with others; (2) the critical importance of mask fit; and (3) the types of air cleaners, of which some are very useful (filters and UV) and others are likely or certainly dangerous (those based on chemistry such as ions, plasmas, and hydroxyls, or those based on spraying chemicals in the air).