A group of 239 scientists from 32 countries have alerted the World Health Organisation to the possibility of COVID-19 being spread through very small droplets (called aerosols) that can stay suspended in the air for long periods of time. Indeed, an early laboratory study carried out by the National Institute of Health in the United States found that the coronavirus can linger in the air for up to four hours in aerosol form. On the basis of this and many more studies, the scientists are warning that WHO and other public health organisations should review their health guidelines on COVID-19.
“The current guidance from numerous international and national bodies focuses on hand washing, maintaining social distancing, and droplet precautions. Most public health organizations, including the World Health Organization (WHO), do not recognize airborne transmission except for aerosol-generating procedures performed in healthcare settings. Hand washing and social distancing are appropriate, but in our view, insufficient to provide protection from virus-carrying respiratory micro-droplets released into the air by infected people,” the scientists say in an open letter they have written to WHO.
Studies by the letter’s signatories and other scientists have demonstrated that viruses are released during exhalation, talking, and coughing in micro-droplets small enough to remain aloft in air and pose a risk of exposure at distances beyond 1 to 2 metres from an infected individual. They warn that the possibility of infection is especially acute in indoor or enclosed environments, particularly those that are crowded and have inadequate ventilation relative to the number of occupants and extended exposure periods.
“For example, airborne transmission appears to be the only plausible explanation for several superspreading events investigated which occurred under such conditions e.g., and others where recommended precautions related to direct droplet transmissions were followed.”
For their part, the scientists propose that in order to control the pandemic, pending the availability of a vaccine, all routes of transmission must be interrupted. The measures they recommend to mitigate airborne transmission risk include the following: providing sufficient and effective ventilation (supply clean outdoor air, minimize recirculating air) particularly in public buildings, workplace environments, schools, hospitals; supplementing general ventilation with airborne infection controls such as local exhaust, high efficiency air filtration, and germicidal ultraviolet lights and avoiding overcrowding, particularly in public transport and public buildings. They note that these measures are practical, can be easily implemented, many are not costly and offer more benefits than potential downsides even if they can only be partially implemented.
“For example, simple steps such as opening both doors and windows can dramatically increase air flow rates in many buildings,” they state in the letter to WHO.
If WHO adopts recommendations made by these scientists, some Third World countries would still not be able to implement some of them. In order to reduce crowding in public transport vehicles, the Botswana government halved the number of passengers. While this measure may have been effective in controlling spread, it also crippled the public transport and was reviewed a day before operators threatened to go on strike.