# Covid-19 decay rates and half-life.



## Ronni (May 18, 2020)

On one of my other threads, someone mentioned concern for me going into Ron's house and the potential for contaminated air and potential covid infection.

I thought I'd posted this information earlier, but I can't find it, so I'm covering this aspect now. We become infected by viral particles remaining on surfaces, aerosols continuing to be suspended in the air etc., which is why we're instructed to sanitize surfaces and wash our hands frequently.  

BUT here's the thing. Yes. The virus can linger on surfaces and in the air, and there have been many studies to test HOW LONG the virus remains alive under various conditions.  BUT the AMOUNT of the virus that made it that length of time was only a FRACTION of its original potency.  Extrapolating from that, immediately after a virus particle was expelled either onto a surface or into the air it's at its most potent, but that potency DEGRADES each minute that the virus remains untouched by cleaning, sanitization etc.  

To add to that, the virus doesn't decrease in potency at the same rate for the entirety of its life.  Enter HALF-LIFE. Half life is the amount of time required for a quantity to fall to half its value as measured at the beginning of the time period.  Or put it another way.....You can calculate the half-life of any substance by the initial quantity of the substance vs the quantity remaining after a measured period of time.  The term is most commonly used in relation to atoms undergoing radioactive decay, but can be used to describe other types of decay, whether exponential or not. The half life of Covid-19 has been studied extensively which is how scientists have been able to determine with a relative degree of accuracy how long it remains active.  

Why is half life important?  Because it enables you to determine when a sample of something is safe(er) to handle, whether it's something radioactive, pathogen, virus, whatever.  Studying the half-life of these things helps determine when it's no longer a threat.  Enough half life periods of Covid-19 renders it ultimately ineffective because it decays more and more rapidly over each half-life period.  

I'm not scientist!!! So this is a very simplistic explanation, for my own understanding and continued educating in this area.  

Here are links to some of the science I studied to understand this stuff.  

Surface stability of Sars-CoV-2

New England Journal study

NEJM original article


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## oldman (May 18, 2020)

I though half-life was the time when a chemical was actually used that it took before it was no longer effective? For example, take the narcotic drug Vicodin or Hydrocodone, which is Vicodin's generic. Vicodin's half-life is about 4 hours, which means that once the pill is taken orally, it will have lost its potency in that amount of time, or 4 hours.


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## Ronni (May 18, 2020)

oldman said:


> I though half-life was the time when a chemical was actually used that it took before it was no longer effective? For example, take the narcotic drug Vicodin or Hydrocodone, which is Vicodin's generic. Vicodin's half-life is about 4 hours, which means that once the pill is taken orally, it will have lost its potency in that amount of time, or 4 hours.


@oldman you can find references to Half life and it’s application to all kinds of things from radioactive particles to the amount of time Coffee stays in the system enough to keep you from sleeping!  I’m not kidding!! There was actually a paper written on that!  But here's one reference I saved that specifically talks about the pharmacological applications.

From Medical.Net
_The elimination half-life of a drug is a pharmacokinetic parameter that is defined as the time it takes for the concentration of the drug in the plasma or the total amount in the body to be reduced by 50%. In other words, after one half-life, the concentration of the drug in the body will be half of the starting dose.

With each additional half-life, proportionally less of the drug is eliminated. However, the time required for the drug to reach half of the original concentration remains constant.

In general, the effect of the drug is considered to have a negligible therapeutic effect after 4 half-lives, that is, when only 6.25% of the original dose remains in the body. 
pharmacokinetic parameter as it provides an accurate indication of the length of time that the effect of the drug persists in an individual.

It can also show if accumulation of the drug is likely to occur with a multiple dosing regimen. This is helpful when it comes to deciding the appropriate dose amount and frequency._

EDITED TO ADD:  I will reiterate that I have zero training in any discipline that makes me even vaguely familiar with this stuff. I graduated high school and went on to business school and learned to type and take shorthand...about as far removed as you can get to any kind of scientific training!  I can't THINK with this stuff the way a scientist can, so I learn bits and pieces, verify the information as much as I am able, then add that bit of information to my store of medical/scientific knowledge.  So please, if you know more, if I'm missing even more chunks of ancillary information than I already know I'm lacking, EDUCATE me!  I think it's obvious that I'm eager to learn as much as I can and would love to be mentored to these fuzzy, esoteric concepts that I'm trying to absorb through my friend Professor Google.


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