Covid-19 Virus and Airborne Transmission

The Covid-19 pandemic has evolved into a second wave, one that seems more severe than the first one. Our understanding of how COVID 19 spreads may help us to understand why Covid- appropriate behavior is important to prevent infection!

Airborne transmission

In the early days of the pandemic, both the medical and scientific community believed that the COVID-19 virus transmits largely through fomites and droplet infection.

1. Fomites are surfaces where the virus lands. Touching them and later touching your nose or mouth increases the chances of inhaling or ingesting the virus into the body.
2. When a person coughs, sneezes, talks loudly, sings, etc, droplets of saliva or mucous containing the virus are spread through the air. Anybody who comes in close contact with such a person (less than 1 meter) is at the risk of inhaling or ingesting the virus. That is precisely why we are all advised to wear masks all the time. This will prevent the droplets from entering the body. The droplets sit on the mask, and the virus in them eventually dies out. Or, only a small portion of the viral load in the droplets enters the body. And if the person’s immunity is fairly good, such a small viral load may not cause infection, or cause a milder infection.

This was the prevailing understanding in the initial months. The mucous and saliva coming out of a person’s nose and mouth are of 2 types – fairly large ‘droplets’ and smaller ‘aerosols’. It was believed that droplets alone contribute to the infection and aerosols cannot because the viral load in them is smaller than that of droplets. This was based purely on historical thinking around diseases such as tuberculosis and measles. The scientific community likes to believe that these diseases are only spread through droplets and not through aerosols. Transmission through aerosols is also called ‘airborne transmission’. So the same standards were applied to the COVID-19 virus also.

However, various studies conducted in the last 1 year have proved otherwise. There is ample proof to suggest that the COVID-19 virus is transmitted through both droplets and airborne transmission.

 

Evidence from Research studies

In fact, a research paper published by a team of scientists and funded by the National Institute for Health Research, Economic and Social Research Council and Wellcome Foundation, supported by the US National Science Foundation has presented ten streams of evidence that the COVID-19 virus spreads primarily by airborne transmission. Droplet or fomite-based infections are lesser in number than originally suspected.

1. Some slaughterhouses, choir concerts, cruise ships, care homes, and correctional facilities were studied. The room size, ventilation in it, behavior of the humans using them, and interactions between them were analyzed. Then the viral load was determined. There was no evidence to suggest that the high viral count was caused by fomite or droplet transmission. It could only happen due to airborne transmission.
2. Hotels where people were quarantined were analyzed. Even when the guests in adjacent rooms did not interact with each other, the viral load was high. This points to long-distance or airborne transmission.
3. Even when people were not coughing or sneezing, the viral load was high. This means even talking normally (not shouting or talking loudly) was causing infections. This was validated by direct measurements made. (Speaking produces thousands of aerosol particles, many of which may contain the virus). This clearly points to airborne transmission. Scientist believe that up to 59% of the cases in the world till date have been caused this way.
4. Transmission of the virus or infection rates is higher indoors than outdoors, especially if the ventilation is poor. This clearly points to airborne transmission.
5. Nosocomial or hospital-acquired infections were documented in some hospitals, clinics, and healthcare centers. Despite everyone wearing PPE, which prevents droplet infection, and adequate sanitation, which prevents fomite infection, the infection rates were high. This clearly points to airborne transmission.
6. Cars used by and rooms occupied by COVID-19 patients were sampled for viral count. Despite all precautions against droplet or aerosol transmission, the viruses remained in the air for up to 3 hours.
7. COVID-19 virus has been found in air filters and air ducts in hospitals treating COVID-19 patients. Needless to say, there is no possibility of droplet or fomite infection in such spots. This clearly points to airborne transmission.
8. Caged animals infected with the Covid-19 virus and caged animals that were not infected were kept separately and connected only by an air duct. Some of the uninfected animals also got infected, eventually clearly pointing to aerosol transmission.
9. High-quality contact tracing from various countries have shown that the infection rates from indoor exposure to the virus was high despite reduced chances of droplet or fomite infection. This clearly points to airborne transmission. In contrast, there is not a single study till date that has established COVID-19 infections do not happen from airborne transmission.
10. People who share the same air (like family or co-workers) have got infected despite adequate protection against fomite or droplet infection. This clearly points to airborne transmission.

So How Does One Protect Oneself?

Going by the above evidence that the COVID-19 virus has spread through the world primarily by airborne transmission, how does one protect oneself? Are wearing masks and social distancing pointless measures?

Not really! When one is outdoors, depending on the wind-flow patterns and the speed at which one is moving, airborne transmission is slightly reduced. But the risk of droplet and fomite infection still remains. That is why wearing masks, social distancing, and sanitizing/washing hands are very effective.

But when one is indoors, chances of airborne transmission increase manifold. So what should one do? The obvious answer is to increase ventilation so that the virus is blown or driven away by air currents. Or at least the viral load is reduced. How to do this?

1. Keep the doors and windows of your home or workplace open as much as possible to increase cross-ventilation.
2. Upgrade your air-conditioning equipment or service them regularly so that they are performing efficiently.
3. Given the fact that ACs recirculate the air in most cases, it’s important to not use the AC 24×7. It’s good to use a mix of natural cross-ventilation and air-conditioning.
4. If you suspect a shop, workplace, or home you are visiting does not have good ventilation or well-maintained AC equipment, do not visit. Avoid such places completely and safeguard yourself.

Conclusion

It’s a matter of time before the scientific and medical communities admit that the Covid-19 virus transmits primarily by airborne transmission. In our own best interests, we should take the precautions listed above to minimize airborne transmission, reduce the viral load, and hence the risk of COVID-19 infection. This is not only desirable but inevitable given the rate at which the virus is mutating and the fact that no vaccine today can guarantee 100% protection against the virus.

 

Kauvery Hospital is globally known for its multidisciplinary services at all its Centers of Excellence, and for its comprehensive, Avant-Grade technology, especially in diagnostics and remedial care in heart diseases, transplantation, vascular and neurosciences medicine. Located in the heart of Trichy (Tennur, Royal Road and Alexandria Road (Cantonment), Chennai, Hosur, Salem, Tirunelveli and Bengaluru, the hospital also renders adult and pediatric trauma care.

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