The airborne transmission of SARS-CoV-2 has long been debated upon. Evidence supporting and negating the airborne transmission too has been stated in various studies. Now, The Lancet has published an article stating 10 points of evidence supporting airborne transmission. This article summarises the statements.

Spreading of an infectious virus

The COVID-19 pandemic has reached its horrifying turn and it continues to affect populations across the globe. As per studies, an infectious virus spreads predominantly through large respiratory droplets that fall quickly. The spread of the virus could easily be reduced by restricting direct contact, cleaning surfaces, physical barriers, physical distancing, the use of masks and wearing high-grade protection.

However, if an infectious virus is mainly airborne, an individual could potentially be infected when they inhale aerosols produced when an infected person exhales, speaks, sings, sneezes, or coughs. Reducing the airborne transmission of the virus requires measures to avoid inhalation of infectious aerosols, including ventilation, air filtration, use of masks whenever indoors, attention to mask quality and fit, and higher-grade protection for healthcare staff and front-line workers.

Airborne transmission of SARS-CoV-2- Ten streams of evidence

1. The super spreading of SARS-CoV-2 and its substantial transmission is considered the pandemic’s primary driver. Detailed analyses of human interactions, room sizes, ventilation, and other variables have shown patterns. For example, long-range transmission and overdispersion are consistent with the airborne spread of SARS-CoV-2.
2. Long-range transmission of SARS-CoV-2 between people in adjacent rooms but never in each other's presence has been documented in quarantine rooms supporting its airborne transmission.
3. The asymptomatic or presymptomatic transmission of SARS-CoV-2 from people who are not coughing or sneezing is likely to account for at least one third, and perhaps up to 59%, of all transmission globally and is a key way SARS-CoV-2 has spread around the world. Direct measurements show that speaking produces thousands of aerosol particles and few large droplets.
4. The transmission of SARS-CoV-2 is higher indoors than outdoors and is substantially reduced by indoor ventilation.
5. Nosocomial infections have been documented in hospitals and health-care setups, where there have been strict contact-and-droplet precautions and use of personal protective equipment (PPE) designed to protect against droplet but not aerosol exposure.
6. Viable SARS-CoV-2 has been detected in the air. A laboratory test even claimed that SARS-CoV-2 stayed infectious in the air for up to 3 hours with a half-life of 1.1 hours. Viable SARS-CoV-2 was identified in air samples from rooms occupied by COVID-19 patients even when no aerosol-generating procedures were carried out. Although other studies have failed to capture viable SARS-CoV-2 (that is because sampling of the airborne virus is challenging), SARS-CoV-2 has been identified in air filters and building ducts in hospitals with COVID-19 patients. Such locations could be reached only by aerosols.
7. Some studies have proven transmission of SARS-CoV-2 from infected, caged animals that were connected to separately caged uninfected animals via an air duct.
8. People have avoided SARS-CoV-2 infection in situations wherein they have shared air with infected people, but this could be due to variation in the amount of viral shedding between infectious individuals and their environmental (especially ventilation) conditions.
9. No study has provided strong or consistent evidence to refute the hypothesis of airborne SARS-CoV-2 transmission.
10. Ease of infection between people in close proximity to each other has been cited as proof of respiratory droplet transmission of SARS-CoV-2. However, close proximity transmission in most cases along with distant infection for a few when sharing air is more likely to be explained by dilution of exhaled aerosols from an infected person.

Conclusion

The authors propose that it is a scientific error to use the lack of direct evidence of SARS-CoV-2 in air samples to cast doubt on airborne transmission while overlooking the quality and strength of the overall evidence base. There is consistent, strong evidence that SARS-CoV-2 spreads by airborne transmission. Although other routes can contribute, the airborne route is likely to be dominant.

Reference: Trisha G et al. Ten scientific reasons in support of airborne transmission of SARS-CoV-2. [Online]. Available from: https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)00869-2/fulltext#articleInformation [Accessed 24 April 2021].