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The World Health Organization (WHO) updated its communication on the airborne transmission of SARS-CoV-2 on 30 April 2021. This article summarizes their current opinion.
The authors of the article Ten scientific reasons in support of airborne transmission of SARS-CoV-2 published in The Lancet on April 15, 2021, concluded that "there is consistent, strong evidence that SARS-CoV-2 spreads by airborne transmission. Although other routes can contribute, we believe that the airborne route is likely to be dominant. The public health community should act accordingly and without further delay." 
On April 30, 2021, the WHO updated their original communication dated December 13, 2021, on the transmission of SARS-CoV-2. Here are the salient points:
Transmissibility of the SARS-CoV-2 virus depends upon various factors such as the amount of viable virus being shed and expelled by a person, type of contact, and the settings and circumstances involved.
- A person can get infected when aerosols or droplets containing the virus released from the mouth or nose of an infected person in the form of particles ranging from larger respiratory droplets to smaller aerosols are inhaled or come in direct contact with the eyes, nose, or mouth of the person.
- Close contact with an infected person typically within 1 meter (short-range).
- Clinical settings where aerosol-generating procedures are performed increases the risk of aerosol transmission.
- Although the presence of viral RNA may not represent replication and infection (as a viable virus capable of transmission and initiating invasive infection is required), the presence of viral RNA in air samples of clinical settings in the absence of aerosol-generating procedures as well as the presence of viable SARS-CoV-2 virus from air samples in the vicinity of COVID-19 patients warns the spread of infection in specific settings and circumstances such as indoor, crowded and inadequately ventilated spaces.
- WHO has described the settings where the SARS-CoV-2 virus spreads more easily using “Three C’s” which represent Crowded places, Close-contact settings, and Confined and enclosed spaces with poor ventilation wherein the risk of COVID-19 spreading is especially high in places where these “3Cs” overlap.
- Touching contaminated surfaces followed by touching the eyes, nose, or mouth without washing hands could also spread COVID-19 infection.
Period of infectiousness of infected individuals :
- Irrespective of whether asymptomatic (infected but never develops any symptoms) or pre-symptomatic (not yet developed symptoms but develops symptoms later), all infected individuals can be contagious and the virus can spread from them to other people.
- The period just before individuals develop symptoms (namely 2 days before they develop symptoms), as well as the early phase of their illness, has been found to be the most infectious stage and people who develop severe disease could also be infectious for longer periods.
Follow your “VOWS” to reduce the risk of infection:
- V – Vaccination: When it’s your turn, get vaccinated and follow the vaccination guidelines.
- O – Opt to avoid the “Three C’s” which represent crowded places, close-contact settings, and confined and enclosed spaces with poor ventilation as well as avoid touching surfaces.
- W - Wear a mask (well-fitting three-layer mask) and wash hands frequently with soap and water or alcohol-based hand rub.
- S - Social distancing: Maintain at least a 1-meter distance from others.
- Greenhalgh T, Jimenez JL, Prather KA, Tufekci Z, Fisman D, Schooley R. Ten scientific reasons in support of airborne transmission of SARS-CoV-2. Lancet. 2021 May 1;397(10285):1603-1605. doi: 10.1016/S0140-6736(21)00869-2. Epub 2021 Apr 15. PMID: 33865497; PMCID: PMC8049599.
- Roadmap to improve and ensure good indoor ventilation in the context of COVID-19. Geneva: World Health Organization; 2021. Licence: CC BY-NC-SA 3.0 IGO. https://www.who.int/publications/i/item/9789240021280.
- Coronavirus disease (COVID-19): How is it transmitted? https://www.who.int/news-room/q-a-detail/coronavirus-disease-covid-19-how-is-it-transmitted.