WHO had stated that the transmission of the virus through air could be possible in certain settings and circumstances.
Coronavirus transmission: Recently, it was reported that as many as 239 scientists across 32 countries wrote to world nodal health agency the World Health Organisation (WHO), bringing up the issue that COVID-19 can remain airborne for some time and can transmit itself. They also reportedly showed evidence that people could be infected due to smaller particles of the virus and hence, there was a need for WHO to revise its earlier recommendations. The paper on this matter, titled ‘It is time to address airborne transmission of Covid-19’, was published in a scientific journal on Monday.
Airborne transmission of COVID-19: What it means
A report in IE explained that the transmission of a respiratory disease like COVID-19 can occur through droplets of varying sizes. If the particles of droplets are larger than five to 10 microns in diameter, they are called respiratory droplets, while those smaller than five microns are known as droplet nuclei. The report added that WHO has so far stated that current evidence suggests that the virus is being transmitted through respiratory droplets as well as contact routes. However, in the new letter, scientists have suggested that transmission through aerosols is also possible.
The report explained that while currently WHO believes that virus is being transmitted through droplets which are produced while speaking, sneezing, coughing, etc. Since these droplets are larger, they eventually succumb to gravity and only travel through the air for one metre, according to WHO. However, in the open letter, the scientists cited evidence that the virus can also transmit in droplet nuclei, and these can travel more than one metre and also stay in the air for a long time. The report states that if this can be established, it would indicate that the transmission risk is higher than previously thought.
Airborne transmission: Is the revelation a new one?
The IE report cited WHO as stating that the transmission of the virus through air could be possible in certain settings and circumstances. Some of the settings include those procedures that lead to the generation of aerosols, bronchoscopy, administration of nebulised treatment, endotracheal intubation, manual ventilation before intubation, open suctioning, disconnecting a patient from the ventilator, turning a patients into a prone position, tracheostomy, cardiopulmonary resuscitation, and non-invasive positive-pressure ventilation, the report stated.
The report further stated that in reference to the report of open letters, the global health agency said that there was a need to carefully interpret the initial findings. It added that if the examination of the evidence being cited has to be conducted, then the researchers would be looking at the specific settings where the virus was found to be airborne, the time duration for which the virus stayed in the air, and if the virus continued to stay infectious for the entire duration.
What would happen if the scientists’ claim is established?
If the claim of the 239 scientists is found to be true, wearing a mask would become all the more necessary. It could also mean that the agencies might recommend N-95 masks, used in hospital settings, to prevent the transmission of the virus through aerosols, depending on the availability of such masks and the health conditions of the people.
COVID-19 aerosol transmission: Evidence so far
The report stated that one of the initial studies, published in the journal Nature, had been conducted in two hospitals of Wuhan, and it looked at SARS-CoV-2’s aerodynamic nature by measuring the viral RNA in aerosols. It was found that while the aerosols in isolation wards and ventilated patient rooms contained very low concentration of the virus, the concentration in aerosols in toilet areas used by patients was higher. The study also found that the levels of airborne virus’ RNA were not detectable in most public areas, except for two areas where crowding could occur. It added that while the infectivity of the virus in the areas of hospitals was not established, the scientists proposed that it could potentially be transmitted via aerosols.
In April this year, US National Institute of Allergy and Infectious Diseases researchers published a correspondence on NEJM, which evaluated the stability of SARS-CoV-2, which causes COVID-19, and SARS-CoV-1, which causes SARS, on various surfaces as well as in aerosols. The correspondence found that the SARS-CoV-2 had remained viable in aerosols for the entire duration of the experiment, i.e. three hours. The study stated that their results implies transmission of the virus through aerosols was possible since it could remain active and infectious for hours.
The WHO had then disagreed with the correspondence’s findings and had stated that the presence of virus in aerosol for up to three hours did not reflect a clinical setting where procedures leading to aerosol generation were being performed, meaning that the study “experimentally induced aerosol-generating procedure”.
Then, in May, the US’ Centre for Disease Control and Prevention (CDC), released a study called “High SARS-CoV-2 Attack Rate Following Exposure at a Choir Practice”. In the study, the researchers studied superspreading events, and established that after a 2.5-hour-long choir practice, which 61 people attended, including one symptomatic index patient, as many as 32 confirmed and 20 probable secondary COVID-19 cases cropped up; three patients had to be hospitalised, while two succumbed.
The study stated that singing itself might have led to the transmission due to the emission of aerosols, which were affected by “the loudness of vocalization”. It added that some people, referred to as super-emitters who generate more aerosols during speech as compared to their peers, might have played a hand in this transmission.