WHO acknowledges airborne transmission of coronavirus in closed settings, and asymptomatic spread

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The World Health Organization on July 9 acknowledged that novel coronavirus can be airborne in closed settings and spread from one person to another in such settings which are poorly ventilated and after prolonged exposure. It also acknowledged that people without symptoms can spread the virus.

The World Health Organization on July 9 acknowledged that novel coronavirus can be airborne in closed settings and spread from one person to another. It also acknowledged that people without symptoms can spread the virus.

The acknowledgment about airborne transmission comes two days after it acknowledged that evidence is emerging on the airborne spread of the virus, after more than 200 scientists wrote an open letter, which was published on July 6 in the journal Clinical Infectious Diseases, appealing to the medical community and national and international bodies to “recognize the potential for airborne spread of COVID-19”.

From its earlier stand that only certain of medical procedures can produce very small droplets, called aerosols, which can remain suspended in air for extended time, the WHO now acknowledges that closed settings where people talk, sing or shout can possibly spread the virus. It has accordingly revised the part about what is known about aerosol transmission where it says: “There have been reported outbreaks of COVID-19 in some closed settings, such as restaurants, nightclubs, places of worship or places of work where people may be shouting, talking, or singing.  In these outbreaks, aerosol transmission, particularly in these indoor locations where there are crowded and inadequately ventilated spaces where infected persons spend long periods of time with others, cannot be ruled out.” But the global body insists that more “studies are needed to investigate such instances and assess their significance for transmission of COVID-19”.

The reversed stand of the WHO is in line with what the experts had expressed in the letter. They had said that it has been “demonstrated beyond any reasonable doubt that viruses are released during exhalation, talking, and coughing in microdroplets small enough to remain aloft in air and pose a risk of exposure at distances beyond one-two metres from an infected individual”. The letter clearly mentioned that the possibility of virus spread is particularly “acute in indoor or enclosed environments” which have poor ventilation and there is extended exposure.

In the updated Scientific Brief, the global health body now says: “WHO, together with the scientific community, has been actively discussing and evaluating whether SARS-CoV-2 may also spread through aerosols in the absence of aerosol generating procedures, particularly in indoor settings with poor ventilation.”

The Brief specifically mentions that “some outbreak reports related to indoor crowded spaces have suggested the possibility of aerosol transmission, combined with droplet transmission, for example, during choir practice, in restaurants or in fitness classes. In these events, short-range aerosol transmission, particularly in specific indoor locations, such as crowded and inadequately ventilated spaces over a prolonged period of time with infected persons cannot be ruled out.”

Asymptomatic spread

After continued refusal to acknowledge spread of the virus by people who do not have symptoms, the WHO reversed its stand. It acknowledged that people without symptoms can spread the virus. Revising the Q&A section on how COVID-19 is spread, the WHO says: “Infected people can transmit the virus both when they have symptoms and when they don’t have symptoms.”

It then goes to advice that asymptomatic transmission makes it all the more important why identifying all people who are infected through testing is carried out and the infected people are isolated and provided treatment based on the clinical condition. It then says: “Even people confirmed to have COVID-19 but who do not have symptoms should be isolated to limit their contact with others.  These measures break chains of transmission.”