Aerosol Transmission of COVID-19

Aerosol Transmission of COVID-19. Jefferson T, Heneghan C.

Published on June 4, 2020

Bottom Line

Transmission of COVID-19 may take place by fine droplets emitted by infected people with no symptoms when they speak or breathe without necessarily coughing or sneezing.

Evidence Summary

This was a descriptive review of reports of COVID-19 transmission suggestive of aerosol transmission, backed by the evidence from laboratory studies and parallels with other viral respiratory diseases. COVID-19 can remain active in aerosol for at least 3 hours, although its concentrations decrease, and aerosols are likely affected by other environmental features that were not assessed.

What did they do?

The authors examined early reports of transmission of COVID-19 from asymptomatic cases.

The identified evidence suggests that fine droplets (smaller than 5 microns) emitted during breathing, talking or even singing could generate a suspension and transmit the agent. Finer droplets being less heavy remain suspended for hours, while larger heavier droplets drop to the ground or surfaces.

They also looked at the experimental and historical evidence for droplet generation, transmission and survival of respiratory viruses, including SARS-CoV 1 and SARS-CoV 2. The aerosol can remain suspended for hours and carried long distances and with thermal currents up elevator shafts and staircases. The fine droplets can also be inhaled deeper into the human airways, finding better conditions for viral replication.

The authors cite one laboratory study finding that COVID-19 can remain active in aerosol for at least 3 hours, although its concentrations decreases over time.

Study reliability

The available evidence reports limited information addressing aerosol transmission for SARS‐CoV‐2.

Clearly defined setting Demographic characteristics described Follow-up length was sufficient Transmission outcomes assessed Main biases are taken into consideration
Yes Yes Yes Unclear No

What else should I consider?

There is limited data to date that have recorded aerosolized SARS virus particles that remain suspended in the air. Further data collection requires assessment under differing conditions of temperature and humidity. This work should be low cost and results available in a relatively short time.

The evidence from this review needs replicating, updating and incorporating into a systematic review with a predefined protocol and a clear search and inclusion strategy.

About the authors

Carl Heneghan

Carl Heneghan

Carl is Professor of EBM & Director of CEBM at the University of Oxford. He is also a GP and tweets @carlheneghan. He has an active interest in discovering the truth behind health research findings

Tom Jefferson

Tom Jefferson

Tom Jefferson is a senior associate tutor and honorary research fellow, Centre for Evidence-Based Medicine, University of Oxford.