June 7, 2021
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With the clamour of scientists growing louder and evidence piling every day, the discussion of airborne transmission of Covid-19 has finally come to a consensus with the CDC and WHO both making the announcement official. The medical bodies have updated their guidelines nearly a month after a report in the medical journal Lancet backed by many scientists claimed that there is strong and consistent proof that the SARS-CoV-2 virus is transmitted predominantly through the air.
What does “airborne” mean, exactly?
Clarifying the meaning of the word “airborne” is a great place to begin considering the amount of panic and misconception this single word has created in the general public—especially in India. The scientific meaning of the word isn’t the same as its commonly used or understood meaning.
“Airborne” does not mean that the SARS-CoV-2 virus spreads in the open air, that outdoor air is dangerous, and that the virus is potentially everywhere around us. No, you also do not need to wear N-95 masks at all times to protect yourself. What it does mean is that the previously accepted theory that the SARS-CoV-2 virus spreads primarily through large droplets that travel only short distances (less than 2m) has been discarded. It is now believed that the virus can travel much farther (close to 10m) and can collect in the air of a closed space in the form of aerosols.
As panic-inducing as it can be to read a news headline that the coronavirus is airborne with the implication that there is seemingly no safe distance between the virus and you, and that risk is nearly unavoidable, it is actually a call-to-action to open your windows instead of closing them.
Droplets or aerosols?
Since the pandemic began, the question of how the coronavirus transmits has been the subject of greatest importance in the effort to curb the virus. It was earlier suggested that the SARS-Cov-2 virus spreads mainly through large droplets that are produced when a person sneezes, coughs, or talks loudly. It was believed that these droplets, since they were of large size, could only travel short distances and fell to the ground. With this understanding, a person standing 2m (6 feet) away was considered safe from viral transmission.
However, by studying contact tracing data over the world, researchers found that the “super-spreader” events tended to occur in venues and events where people tended to linger longer: in offices, conferences, retail stores, indoor restaurants, and most importantly, homes. Transmission was found to be more likely when people spent more time together in a closed environment. Over time, the evidence for aerosol-based airborne transmission became overwhelming, and that for droplet transmission hard to find.
Experts over the world are now of a collective opinion that public health measures that fail to treat the virus propagation predominantly through airborne transmission leave the public unsafe and allow the virus to spread.
What is the new advisory?
The US Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO), and Union Health Ministry (India) have recognised that SARS-Cov-2 is airborne and can be transmitted through respiratory fluids, which are fine droplets or aerosols that are released during respiration. This means that the SARS-CoV-2 virus can be transmitted when an individual inhales respiratory aerosols produced when a COVID-infected person exhales (including quiet breathing), talks, sneezes, coughs, sings, or shouts. Public guidelines now include “airborne transmission” as a possible mode of coronavirus transmission.
These aerosols or respiratory droplets that carry the SARS-CoV-2 virus and transmit infect exist across a spectrum of sizes. The virus can travel on very small particles that can build up indoors but disperse quickly and easily outdoors. Indoors, these particles can travel much farther than the stipulated social distance of 2m (6 feet). These exhaled respiratory fluids can settle on surfaces or remain suspended in the air, building up. Although large droplets settle down to the ground within seconds to minutes, the very small droplets and aerosols can remain suspended for minutes to hours in a poorly ventilated space.
This is why the straightforward public health messaging in Japan is to avoid the 3 Cs—closed spaces, close contact, and crowds.
What should you do, especially regarding indoor ventilation?
The risk of transmission increases greatly in closed, poorly/ unventilated spaces because respiratory fluids and aerosols can quickly spread and concentrate in such areas. You should keep your indoors well-ventilated by keeping windows and doors open to ensure good air circulation and by using exhaust systems.
It is repeatedly stressed that the risk of coronavirus transmission is markedly lower outdoors because virus-carrying aerosols dissipate quickly in the open air. It is advised that you take measures to improve ventilation in homes, offices, and public spaces. Simple and strategic placement of fans, open windows and doors, and exhaust systems introduce outdoor air and improve the quality of air inside. Creating cross-ventilation goes a long way in curbing the transmission of Covid-19.
Therefore, indoor spaces such as indoor restaurants where mask protection is compromised while eating and have plexiglass separators to create a physical barrier between diners don’t actually provide much protection against viral transmission. We have also enjoyed a false sense of security with a social distance of 6 feet and the “sanitisation theatre” in airports, public offices, and other public spaces. A focus on ensuring good ventilation and should be a much bigger priority than the manic disinfection of all surfaces and store-bought items.
These precautions are underpinned, of course, by continued use of face masks and hand washing/ sanitisation.
In the face of it, the new advisory may seem contradictory to earlier precautions. But digging deeper into the CDC and the Indian government advisory, we see that the breadth of precautions has only been expanded, and they do not contradict earlier guidelines. Transmission of Covid-19 being considered airborne does not indicate in any way that outside/ open air and ventilation are the new public enemy. In fact, it only reiterates the knowledge that closed spaces and close contact are where the SARS-Cov-2 virus is transmitted most easily, and that good ventilation and open spaces combined with mask wearing and vaccination are the most potent weapons against Covid-19.