Which Coronavirus Is Most Infectious?

The comparison of short-term aerosol efficiencies of 3 coronaviruses showed the newest one, Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), remained infectious the longest.

A study published in Emerging Infectious Diseases on June 23, 2020, suggests that SARS-CoV-2 generally maintains infectivity at a respirable particle size over short distances, in contrast to either betacoronavirus, SARS-1 and the Middle East respiratory syndrome (MERS). 

Aerosol suspension results suggest that SARS-CoV-2 persists longer than would be expected when generated as this size particle (2-µm mass median aerodynamic diameter). 

This finding is notable because decay and loss in the infectious fraction of airborne virus would be expected on the basis of prior susceptibility studies with other environmentally hardy viruses, such as monkeypox virus.

A recent study showing only a slight reduction of infectivity in aerosol suspensions with approximately similar particle sizes also suggested minimal effects on SARS-CoV-2 airborne degradation.

Collectively, these preliminary data suggest that SARS-CoV-2 is resilient in aerosol form and agree with conclusions reached in earlier studies of aerosol fitness. 

A clear limitation of the aerosol stability data is that we report only 1 measurement of the 16-hour time point. 

Specifically, virions aged for 10-minutes or 16-hours were similar in shape and general appearance to virions examined in samples of viral inoculum collected before aerosolization, which is consistent with the retention of replication-competence and suggests the potential to be infectious after long-term aging in aerosol suspension.

Future studies need to repeat these findings before any definitive conclusions are reached, stated these researchers.

Aerosol transmission of SARS-CoV-2 may be a more important exposure transmission pathway than previously considered. 

This approach of quantitative measurement of infectivity of viral airborne efficiency augmented by assessment of virion morphology suggests that SARS-CoV-2 may be viable as an airborne pathogen.

Humans produce aerosols continuously through normal respiration. 

Aerosol production increases during respiratory illnesses and during louder-than-normal oration.

A fraction of naturally generated aerosols fall within the size distribution used in our experimental studies (<5 μm), which leads us to conclude that SARS-CoV-2–infected persons may produce viral bioaerosols that remain infectious for long periods after production through human shedding and airborne transport. 

Accordingly, this study results provide a preliminary basis for broader recognition of the unique aerobiology of SARS-CoV-2, which might lead to tractable solutions and prevention interventions, concluded these researchers, in the Volume 26, Number 9—September 2020, early release edition.

This work was supported by the Intramural Research Program of the NIAID, NIH, and the Office of the Chancellor at the University of Pittsburgh. Work performed at Tulane National Primate Research Center was supported in part by NIH grant no. P51OD011104. R.F.G. was supported by NIH grant no. U19AI135995. Work at the University of Texas Medical Branch was supported by NIH grant no. R24AI120942. The Defense Health Program provided the funding for SARS-CoV-2 work in USAMRIID. The work at NIH-IRF was funded in part through NIAID, Division of Intramural Research and Division of Clinical Research, Battelle Memorial Institute’s prime contract with NIAID under HHSN272200700016I and in whole or in part with federal funds from NIAID, NIH, US Department of Health and Human Services, HHSN272201800013C. J.K.B. performed this work as an employee of Battelle Memorial Institute. M.G.L. performed this work as an employee of Lovelace Respiratory Research Institute and Laulima Government Solutions, LLC.

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