Reader Charles sent me a linking to a publicly-available article from the New England Journal of Medicine that measured the viability of the Cov-19 virus (they call it SARS-CoV-2, or “severe acute respiratory syndrome coronavirus-2”) on various surfaces, comparing it to the viability of a closely related coronavirus, SARS-CoV-1. You’ll remember the second virus from a while back since it was the cause of SARS. As the NIH notes:
SARS-CoV-1, like its successor now circulating across the globe, emerged from China and infected more than 8,000 people in 2002 and 2003. SARS-CoV-1 was eradicated by intensive contact tracing and case isolation measures and no cases have been detected since 2004.
The very short article is intelligible to laypeople, and you can see it here or by clicking on the screenshot below. The full reference is at the bottom:
To measure the viability in aerosols, the virus was nebulized (put into an aerosol form of small droplets), and squirted into a “Goldberg drum,” which rotates and keeps the nebulized material in the air for a long time. Here’s one of those drums from ResearchGate:
At various intervals, the infected material was sampled and tested for virus viability (aerosol from the drum or virus sprayed on surfaces of copper, cardboard, plastic, and stainless steel). The remaining amount of virus capable of causing infection was measured as the TCID50, or the amount of sampled material required to cause infection in 50% of tissue-cultured material. This figure drops over time as the virus dies.
The main lesson comes from the figure below, which gives, in the three rows, the decay of viable virus over time, the regression plots (on a log scale) predicting the decay over time, and the estimates of the half-life of the virus in aerosols and on various surfaces based on assuming an exponential decay rate of the virus quantity. The virus of interest, SARS-CoV-2, is shown in red, and its relative the SARS virus (SARS-CoV-1) is in blue.
Have a gander. I’ve put the journal’s caption below the figure for mavens, but summarize the results below that:
1.) The new virus has a decay rate about the same as the old SARS virus—except on cardboard. The new Covid-19 virus decays completely on cardboard after 24 hours, but the earlier virus is pretty much gone after only eight. What this means is that if you get a cardboard package in the mail from a place like Amazon, either have it left outside your door or, if you’re worried, handle it with gloves and then don’t open it for at least a day.
2.) On stainless steel and plastic, the new virus will be almost completely gone after four days, and on copper in about 8 hours. This means that if you’re holding onto stainless steel or plastic, as in subway straps or poles, or steel banisters, you could be infected even several days after an infected person touched those surfaces.
3.) The new virus in aerosols was even less viable than on cardboard, with both old and new viruses having a half life of one hour (i.e., after 8 hours the infectability has been reduced by 256-fold). But still this means that if you walk through a space in which an infected person has sneezed or coughed an hour or two beforehand, you could get infected.
The main lesson is to avoid being near people sneezing and especially coughing, and wash your hands ASAP if you’ve touched anything suspicious. And, of course, DO NOT TOUCH YOUR FACE. I’ve been practicing that and, I think, have gotten pretty good, though we all touch our faces unconsciously.
Here’s a photo from the NIH, showing the virus erupting from cells. The caption: “NIAID-RML.”
van Doremalen N. et al. 2020. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. New England J. Med. March 17, 2020; DOI: 10.1056/NEJMc2004973.