# SARS-COV-2 decay on various common substances - How to interpret?

There are two studies that I am aware of that have published SAR-COV-2 virus persistance on various substances Lancet April 2 2020 and New England Journal of Medicine Marc 17 2020.

My question deals with the interpretation of the data presented, particularly in light of media (NBC, CBS, etc.) providing advice and answering questions of the public.

Focusing on two particular assertions: 1) currency (folding bills) are not likely to be an source of transmission. ("no need to clean bills received from unknown sources") 2) Aerosolized virus will become impotent after 3 hours.

In the first instance, that of currency, the Lancet paper did inoculate bank notes and after 2 days there was still detectable virus on the bank notes. Measurement after 4 days, the virus level was undetectable.

In the second instance, with regard to aerosolized virus, the New England Journal paper appears to have suspended the experiment at 3 hours, but at 3 hours there was still a detectable level of virus present (albeit at half the initial level).

Now, here is where I'd like help: In both papers, the researchers measured the "Virus Titre, with the dimensions of "TCID 50". Is there some meaning to that dimension, that I'm overlooking?

To assist here are two examples:

• The units in the Lancet chart are "log TICD50", and the graphs in the NEJM paper are scaled in units of 10^whatever. Both are on a logarithmic scale, not a linear one.
– Mark
Apr 9, 2020 at 0:28
• @Mark. So using the the banknote as an example: t=0, concentration is approx 1.1 million units, at t=2 days, the concentration is approx 300 units. Is that correct?
– BobE
Apr 9, 2020 at 3:48
• @Mark, and using the NEJM example (approximating from graph) time =0 , concentration is 1x10^3 and at time= 3hrs concentration is 1X10^2. Is that a correct approximation?
– BobE
Apr 9, 2020 at 3:58
• Reasonably correct, yes, though I don't know if the Lancet paper is using the base 10 log or the natural log (it doesn't really matter -- the trend is the same either way).
– Mark
Apr 9, 2020 at 20:16

The TCID50 (Median Tissue Culture Infectious Dose) is one of the methods used when verifying viral titer.

TCID50 signifies the concentration at which 50% of the cells are infected when a test tube or well plate upon which cells have been cultured is inoculated with a diluted solution of viral fluid.

So, in the second paper they're talking about the amount of virus in a litre of air that has been aerosolized from these concentrations of virus fluid

Clearly different countries responded differently

The Guangzhou branch of China’s central bank says it will destroy all banknotes collected by hospitals, wet markets and buses to ensure the safety of cash transactions as the country battles a coronavirus outbreak.

https://www.zeomic.co.jp/en/glossary/virus/71

https://www.scmp.com/economy/china-economy/article/3050868/fresh-cash-old-china-central-bank-branch-destroy-banknotes

• Appreciate it, my conclusion (layman's) is that banknotes (of unknown origin) are not intrinsically "safe" before 4 days, and that aerosol viral shedding is remains dangerous after 3 hours (at 22C/40%RH)
– BobE
Apr 8, 2020 at 5:27
• Well, the CDC/WHO position has been that aersol virus is not important ... which is likely to be incorrect. Apr 8, 2020 at 5:31