How long does the coronavirus last on surfaces?

It all depends on what surface it is, and how many virus particles landed on it.

Welcome to Not a Doctor, the only newsletter about health and science that reminds you to leave your shoes at the door.

I’m Melody Schreiber, a journalist and the editor of What We Didn’t Expect. I’m not a doctor, or a scientist, or really an expert of any kind. I just like to ask questions and try to find the answers to them.

Today, we’re getting nerdy about how long virus particles last on surfaces. Yes, I’m extremely fun at parties, why do you ask?

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A few quick definitions

Before we get started, shall we have a little refresher on terms?

SARS-CoV-2 is a virus belonging to the coronavirus family.

Covid-19 is the illness caused by SARS-CoV-2.

While SARS-CoV-2 can cause Covid-19, not everyone who has the virus gets the illness. Some people are entirely asymptomatic. 

I call SARS-CoV-2 “the coronavirus” because it’s a bit easier on the ears (and because it is the coronavirus of the times), but there are several other types of coronaviruses.

For instance, there’s SARS-CoV-1, a different but pretty similar coronavirus. They're siblings in the same family.

Also, I use the term “viable” a few times below. Viruses are “viable” when they’re still infectious.

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So much depends on the surface — and the source

A study published in the New England Journal of Medicine examined how long both SARS viruses lasted on surfaces — namely, on plastic, stainless steel, copper, and cardboard.

(This study also looking at how long the virus can last in artificially created aerosols — we can talk more about that in another update.)

The best material was copper, which has some antimicrobial properties; the virus only lasted for four hours on copper. Why aren’t more things made with copper?!

Next was cardboard; the virus lasted for one day (24 hours), although the researchers said the data were “noisier” — meaning, harder to interpret — for cardboard, making it subject to change. That may mean the actual time is less; SARS-CoV-1, for comparison, only lasted for eight hours on cardboard.

On stainless steel, low amounts of viable virus particles were still detectable after two days. On plastic, some small amounts of viable viruses were still there after three days.

Another study, published in The Lancet Microbe, found that the virus wasn’t viable on paper and tissue after three hours. On cloth and wood, the virus didn’t last beyond one day. On glass and currency, the virus was gone after three days. On plastic and stainless steel, it was gone after a week.

With the exception of copper, it seems like the smoother the surface, the longer virus particles remain viable.

However, there’s one factor that’s very important to consider here. The virus loses its viability in regular increments — with a half-life of one to six hours, depending on the surface.

Here’s why that’s important: If there’s a ton of virus particles on a surface, the odds are higher that some will remain viable and that you’ll come into contact with them, versus if there are only a few particles hanging out here and there.

So, if we’re talking about a hospital bed or a bathroom used by someone with a severe case of Covid-19, yeah, it’s probably gonna be contagious for a few days. But if, say, a mail carrier handles a package briefly without coughing or breathing on it, it’s less likely to be contagious for as long.

And the longer you wait to handle a potentially contaminated item, the less likely it is to get you sick. So even if you’re not able to wait 24 hours to bring that box inside, 12 hours later is better than right away.

This newsletter officially stans copper. Image: Massimiliano Calamelli

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Also, let’s talk about shoes

One study detected virus particles on the floor of a pharmacy, even though no patients had been to the pharmacy. The researchers concluded that the virus must’ve hitched a ride on the shoes of people caring for Covid-19 patients. If a patient coughed and the droplets landed on the floor, a nurse or doctor or specialist likely tracked the virus to other floors.

So what do you do with that information? Do you need to sanitize your shoes constantly?

If you work in a hospital, yes; hit those suckers with some Lysol spray every time you leave the Covid floor.

For everyone else, you probably shouldn’t waste the Lysol unless you’re pretty sure you’ve been around sick people. And definitely don’t try to wipe your shoes off with wipes or a washcloth; odds are, you’d just contaminate your hands and spread any virus particles around.

Instead, just take your shoes off at the door and then wash your hands. When you put your shoes back on to go outside later, make sure you don’t touch the soles, but the laces should be fine unless you have a habit of walking around with your shoes untied.

And it wouldn’t hurt to wash your shoes in hot water every now and then. (I’ll talk about the roles of heat and UV light in killing the virus in an update soon!)

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As always, please leave a comment or email me with questions and feedback at melodyaschreiber@gmail.com. I love hearing from readers!

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