October 12, 2020

expert reaction to study looking at how long the SARS-CoV-2 virus can last on surfaces in the dark and at different temperatures

A study, published in the Virology Journal, looked at how long the SARS-CoV-2 virus can last on surfaces in the dark and at different temperatures.

Dr Julian Tang, Honorary Associate Professor in Respiratory Sciences and Clinical Virologist, University of Leicester, said:

“This is yet another study of SARS-COV-2 survival on various surfaces – following on from these earlier studies: https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247(20)30003-3/fulltext and https://www.nejm.org/doi/full/10.1056/nejmc2004973.

“Unfortunately, there are no standard, consensus ways of performing such studies – which have been performed for influenza as far back as the 1980s: https://pubmed.ncbi.nlm.nih.gov/6282993/; and more recently for 2009 pandemic flu: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0027932; and for the SARS 2003 and other common cold coronaviruses: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7107832/ and https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4659470/pdf/mBio.01697-15.pdf

“This recent Australian study:

– contaminated various surfaces with cell-cultured SARS-COV-2 in African green monkey kidney-derived Vero E6 cell – so not using virus obtained directly from human patient clinical samples;

– mixed the cultured SARS-COV-2 virus with a ‘matrix’ solution containing bovine (derived from cows) proteins to mimic human saliva/mucous;

– at viral loads for SARS-COV-2 essentially similar to those found in human saliva/spit.

“This is a fairly typical lab-based approach, but both the virus (passaged through non-human Vero E6 cell lines) and the ‘matrix’ may not be truly representative of typical human SARS-COV-2 shedding – which is subject to rapid human innate/specific immune responses and clearance in saliva/mucous.

“Also, if the initial SARS-COV-2 surface contamination is via smaller exhaled droplet aerosols landing on surfaces (much more common) than from just a saliva/mucous-contaminated fingers, the viral loads in aerosols are usually lower – perhaps about 1000-10,000 times lower, based on similar studies on influenza.  Although these lower aerosol viral loads may be enough to cause transmission via inhalation (i.e. directly to cells in the respiratory tract bearing ACE2 SARS-COV-2 receptors), this same viral load on surfaces from aerosol deposition is likely not enough to transmit via hand-to-surface-to-mouth/nose route, as human sweat, saliva, mucous all have natural antiviral properties which are not present in the virus ‘matrix’ in this study.

“In fact the whole approach/optimisation of such lab-based viral culture studies/experiments deliberately try to enhance virus survival – whereas our bodies’ natural immune defences do the opposite.

“So whilst such survival may be possible to demonstrate in the lab, in real-life everyday situations, such long survival periods may not be realistic.

“Also, if people are wearing masks – they cannot self-inoculate to their nose/mouth easily (touching eyes is less common and eye fluids also have antiviral properties) – and people should be washing/alcohol gelling their hands more frequently now, anyway.”

Prof Paul Digard, Chair of Virology, and Head of the Division of Infection & Immunity, The Roslin Institute, University of Edinburgh, said:

“This is a good quality study that measured infectious virus, not just detectable bits of virus.  It makes an important point that the virus CAN survive in an infectious form for quite long periods of time on commonly-handled objects – what’s important to remember however, which hasn’t featured in the media coverage I’ve seen so far, is that the infectivity decays over time.  So the amount of virus surviving at 28 days is very low and is therefore likely to be much less likely to infect someone than the higher amounts present when the virus is freshly deposited.”

‘The effect of temperature on persistence of SARS‑CoV‑2 on common surfaces’ by Shane Riddell was published in the Virology Journal.

DOI: 10.1186/s12985-020-01418-7

https://link.springer.com/epdf/10.1186/s12985-020-01418-7

Declared interests

None received.