One of the main ways in which the coronavirus spreads is through respiratory droplets when an infected person coughs, sneezes, talks, or breathes.

These droplets can land on surfaces or objects, where they can survive for hours or even days, and infect other people who touch those surfaces and objects and then touch their mouth, nose, or eyes. However, recent studies and cases have also suggested that the virus can spread through the air, especially in certain settings and circumstances.

What do we know about airborne transmission?

According to the World Health Organization (WHO), airborne transmission refers to the transmission of an infectious agent in small particles known as aerosols that can remain suspended in the air for long periods of time and can be inhaled by other people in the same space. Aerosols can be produced by activities such as talking, singing, shouting, coughing, and sneezing, and can travel farther and stay in the air longer than respiratory droplets.

While the WHO and other health organizations initially downplayed the possibility of airborne transmission of the coronavirus, citing the lack of strong evidence and the fact that most infections were traced back to close contact with infected people, recent findings have raised concerns and prompted more research and recommendations.

What are the factors that contribute to airborne transmission?

The airborne transmission of the coronavirus is more likely to occur in certain settings and circumstances where the following factors are present:.

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• Enclosed spaces with poor ventilation, such as offices, classrooms, restaurants, and public transportation vehicles, where the concentration of aerosols can build up and linger.
• Extended exposure to a high concentration of aerosols, such as during a long meeting, a choir practice, a fitness class, or a crowded bar.
• Activities that generate more aerosols, such as singing, shouting, heavy breathing, and playing wind or brass instruments.
• Close proximity to an infected person who is producing aerosols, such as in a hospital room, a household, or a nursing home.

What are the implications of airborne transmission?

If the coronavirus can spread through the air, it has significant implications for how we can protect ourselves and others from infection. Some of the key concerns and recommendations are:.

• Wearing a mask or face covering is even more important, as it can reduce the emission and inhalation of aerosols. However, not all masks are equally effective against aerosol transmission, and some types of masks may even increase the dispersion of aerosols. The WHO recommends the use of medical masks or respirators in specific settings and circumstances.
• Maintaining physical distance of at least 6 feet may not be sufficient to prevent airborne transmission, especially in enclosed spaces with poor ventilation. Increasing the ventilation of indoor spaces can help dilute and disperse aerosols, and using portable air cleaners with HEPA filters can also be effective.
• Avoiding crowded, enclosed, and poorly ventilated spaces, especially for extended periods of time, can lower the risk of airborne transmission.
• Following good hygiene practices such as frequent hand washing, covering coughs and sneezes, and avoiding touching one’s face can also reduce the risk of infection, but may not be sufficient to prevent airborne transmission.
• Testing and contact tracing can help identify and isolate infected people before they can spread the virus through the air.

What are some examples of airborne transmission?

There have been several notable cases and clusters of coronavirus infection that have been attributed to airborne transmission:.

• A choir practice in Washington state in March 2020, where about 60 people gathered for a 2.5-hour rehearsal in an enclosed space with no masks or distancing, resulted in 32 confirmed cases and 2 deaths, with most likely due to aerosols from singing and speaking loudly.
• An outbreak in a restaurant in Guangzhou, China in January 2020, where one infected person who had no symptoms at the time and sat at a table about 6 feet away from other patrons, infected 9 other people at nearby tables who were not in close contact, likely due to airborne transmission through the air conditioning system.
• An outbreak in a bus in Hunan, China in January 2020, where one infected person who traveled on the bus for about an hour and did not have direct contact with other passengers, infected 13 other passengers who were not in close contact, likely due to airborne transmission in the confined and poorly ventilated space.

What are some ongoing studies and debates on airborne transmission?

There are still many unknowns and controversies surrounding airborne transmission of the coronavirus, and many studies and debates are ongoing. Some of the current topics and issues include:.

• The size and concentration of aerosols that can transmit the virus, and how they vary depending on the activity, environment, and individual factors. Some studies have suggested that even normal breathing and speaking can generate aerosols that carry the virus, while others have argued that the threshold for infectious aerosols is much higher.
• The role of asymptomatic and pre-symptomatic carriers in airborne transmission. Some experts have claimed that these carriers can emit just as many aerosols as symptomatic patients, while others have downplayed their contribution to airborne transmission.
• The effectiveness of different types of masks and ventilation systems in reducing airborne transmission, and how to balance the benefits and costs of these interventions. Some experts have called for more rigorous air quality and ventilation standards in indoor spaces, while others have warned of the potential energy consumption and environmental impact of these measures.
• The need for more guidance and regulations on airborne transmission from health organizations and governments, and how to communicate and implement these recommendations to the public and stakeholders. Some experts have criticized the slow and inconsistent response to airborne transmission, while others have cautioned against overreliance on a single transmission mode.

Conclusion

The question of whether and how the coronavirus can spread through the air is still a topic of intense research and debate, but the evidence and cases suggest that it is possible and can pose a significant risk, especially in certain settings and circumstances.

To protect ourselves and others from airborne transmission, we need to follow the latest recommendations and guidelines from health organizations and governments, and adapt our behaviors and environments to reduce the emission, concentration, and inhalation of contagious aerosols.