May 28, 2020

expert reaction to perspective piece on reducing transmission of SARS-Cov-2

A perspective piece, published in Science, discusses reducing transmission of SARS-Cov-2.

Prof Jonathan Reid, Professor of Physical Chemistry at the University of Bristol, said:

“This perspective article recognises the concern of researchers that aerosols and droplets can transmit SARS-CoV-2 further than the prescribed social/physical distancing guidance. This is particularly true for small respirable particles (<5 micrometres in size) that can remain airborne for some time and travel some distance. In an indoor environment, infectious aerosol concentrations could increase over time, as the paper suggests, dependent on ventilation etc. This article cites a recent study that compares the reduction in exhaled viral copy numbers (the signature of the virus) from influenza and a coronavirus (not SARS-CoV-2) when someone wears a surgical mask, suggesting surgical masks could reduce transmission from an infected individual. Along with other evidence, this suggests that wearing face masks might be a valuable public health measure.

“However, there remain many uncertainties that require urgent research, some of which the paper identifies:

– Although a growing number of papers report identifying the signature of the virus (the RNA copy number) in air samples, this is not the same as reporting/identifying an airborne infectious virus. There is not yet a single report of infectious SARS-CoV-2 virus sampled from air. This is essential to better understand the relative importance of the different modes of transmission. 

– Even if the virus can remain infectious while airborne, the viral load in aerosols and droplets for SARS-CoV-2 is not known. This is important to establishing the possible dose of the virus that someone might be exposed to over a period of time. We don’t yet know what the dose needs to be for an individual to become infected.

– We also don’t know how quickly the infectivity of the virus decays away while airborne and how this depends on the environment (relative humidity and temperature), there are only very limited studies.

– The efficacy of different types of face masks to protect susceptible (uninfected) individuals on inhalation remains unclear and work is needed. The process of inhaling through a face mask is very different from exhaling (the focus of the paper cited above) and, for example, requires the face mask to be tightly fit.”

“Reducing transmission of SARS-CoV-2” by Kimberly Prather et al. was published in Science on 27 May

All our previous output on this subject can be seen at this weblink:

www.sciencemediacentre.org/tag/covid-19

Declared interests

None received.