- The dominance of airborne transmission is supported by long-range transmission observed at super-spreader events.
- Long-range transmission has been reported among rooms at COVID-19 quarantine hotels, settings where infected people never spent time in the same room.
- Asymptomatic individuals account for an estimated 33% to 59% of SARS-CoV-2 transmission, and could be spreading the virus through speaking, which produces thousands of aerosol particles and few large droplets.
- Transmission outdoors and in well-ventilated indoor spaces is lower than in enclosed spaces.
- Nosocomial infections are reported in healthcare settings where protective measures address large droplets but not aerosols.
- Viable SARS-CoV-2 has been detected in the air of hospital rooms and in the car of an infected person.
- Investigators found SARS-CoV-2 in hospital air filters and building ducts.
- It is not just humans — infected animals can infect animals in other cages connected only through an air duct.
- No strong evidence refutes airborne transmission, and contact tracing supports secondary transmission in crowded, poorly ventilated indoor spaces.
- Only limited evidence supports other means of SARS-CoV-2 transmission, including through fomites or large droplets.
1.) Covid-19 has redefined airborne transmission. BMJ 2021; 373 doi: https://doi.org/10.1136/bmj.n913 (Published 14 April 2021) Cite this as: BMJ 2021;373:n91 https://www.bmj.com/content/373/bmj.n913