WHO experts tell Al Jazeera coronavirus may spread through the air in crowded indoor spaces with poor ventilation.
The new coronavirus can possibly be transmitted through the air in crowded indoor settings with poor ventilation such as restaurants, gyms, night clubs and offices, the World Health Organization (WHO) has said, as lockdown restrictions are being eased globally.
The health agency on Thursday published an updated scientific brief on the different modes of transmission of COVID-19, the highly contagious respiratory disease caused by the coronavirus, identifying the different locations and circumstances of virus spread.
According to the WHO, the coronavirus is primarily transmitted by droplets through direct or close contact with an infected person and indirect contact through contaminated surfaces, also known as fomite transmission.
But the possibility of airborne transmission, combined with droplet transmission, cannot be ruled out in specific settings and more research is needed, it said.
In an exclusive interview with Al Jazeera, the WHO’s technical lead on COVID-19, Maria Van Kerkhove, and the agency’s chief scientist, Soumya Swaminathan, talked about the possible ways of COVID-19 transmission, the risks and the preventive measures.
Al Jazeera: Can you explain how airborne transmission takes place exactly and under what circumstances and environments does it pose a higher risk?
Maria Van Kerkhove: Airborne transmission has to do with the size of the droplets that are expelled from people, how long they can be suspended in the air and the distance they can potentially travel. Because they are lighter than respiratory droplets, they can travel through the air further than heavier droplets that tend to fall to the floor much quicker.
We know there can be aerosol transmission in healthcare settings where specific medical procedures, called aerosol generating procedures, are conducted on sick patients.
There’s also the possibility that there could be these smaller particles that come out of people’s mouths when they talk, sing and engage in fitness activities.
Soumya Swaminathan: This is not a virus that’s just floating around in the air and is going to come and infect you – it does require prolonged contact with infected people.
We sometimes refer to these so-called airborne transmission events as super-spreading events, because in these closed environments there have been situations where people get infected – at the meat-packing plants, the choir practice, the night club, the dormitories.
These are spaces where people spend a lot of time together, in poorly ventilated settings and in close proximity. In that situation, if you have someone who is quite infectious and who is either coughing or even just singing even and talking loudly, droplet, contact and fomite transmission can occur, but small particles could be around in that air for some period of time – it’s being together in that environment that is risky.
Al Jazeera: From your research and the evidence collected, how much has the aerosol mode of transmission contributed to the pandemic so far and how do the risks of airborne spread compare with droplet transmission?
Van Kerkhove: From all the available data in all the observational and epidemiologic studies, and the experiences of member states that report to us, the predominant mode of transmission is through droplets and contact. There may be airborne transmission happening in specific closed settings but the extent of that seems to be small. However, there’s a lot of research ongoing in this area, and evidence supports that transmission is predominantly through the droplets and prolonged contact.
Al Jazeera: Is the possibility of airborne transmission a cause for additional concern for the public?
Swaminathan: It’s one more mode of [transmission]. We’ve been laying out the precautions that people need to take and also what the public health authorities need to do. With offices, workplaces and recreational places opening up, people need to remember that these are all the different modes of transmission that you need to be careful about and take precautions against.
While I think many people appreciate the importance of handwashing and respiratory etiquette, perhaps what they forget is that when they gather together in these closed and crowded settings that they can still transmit if they are not maintaining the appropriate physical distance.
Soumya Swaminathan, WHO’s chief scientist
The first thing is to improve ventilation in closed settings like offices, shops and workplace settings. A simple way of doing this is by opening doors and windows and ensuring good air circulation.
If ventilation cannot be improved, then people should avoid such places or wear face masks when they are in close proximity to people – whether its public transport or in shops.
Al Jazeera: Are you reviewing your guidelines?
Van Kerkhove: Yes, constantly. As more information becomes available, we always look at the guidance and we aim to update all of our guidance regularly.
Swaminathan: In fact, we are working on the clinical treatment guidelines now and our guidelines’ development group people is meeting almost every day to provide an update on the use of steroids, on the use of hydroxychloroquine and other drugs.
Thanks to the huge volume of research on COVID-19, it is our endeavour to constantly keep up with emerging data, to analyse and synthesise the evidence and use that to update our guidance.
Al Jazeera: Specifically for airborne transmission, what potential measures are recommended to protect yourself?
Van Kerkhove: Where we know that there could be aerosol transmission, like in medical procedures, we recommend airborne precautions. These are specific types of Personal Protective Equipment that people who are actually performing the procedure and are working in that setting have to wear.
In other situations outside of healthcare facilities, there is a comprehensive package of measures that need to be adhered to in all countries. This starts with identifying cases – symptomatic and asymptomatic – so they could be isolated and cared for quickly.
It also includes identifying the close contacts of infected people so that they could be quarantined in appropriate facilities or safely at home. It includes the use of fabric masks in specific settings where you cannot do physical distancing, where you could have crowding and poor ventilation. We also recommend the usual hand hygiene and respiratory etiquette always – and trying to avoid crowded situations, to begin with.
This interview has been edited for brevity and clarity.
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