How long does the coronavirus last in the air? The latest you need to know

How long does the coronavirus last in the air? The latest you need to know

May 7, 2020 0 By Santiago
Reading Time: 7 minutes

Although I’m happy that they finally let us out for an hour a day in our part of the world, I’m sick of wearing a surgical mask whenever I go out running. It’s annoyingly hard to breathe through. All because my saliva may dwell in the air long enough to expose my surroundings with the COVID-19-causing coronavirus SARS-CoV-2.

OK, I’ll admit that I gladly put on that cursed mask as long as it can protect my surroundings. When we speak, we release tiny saliva droplets or so-called aerosols, which are microscopic particles. Aerosols can attach to, for example, dust and are so small that they stay in the air for longer times than larger droplets. In other words, there’s a chance that I’m sharing my nasty saliva with all of you while running. So, I’ll keep wearing my mask and just carry on.

But all these guidelines and “rules” also triggered my curiosity. How long does the coronavirus last in the air if you release it through breathing or talking? The answer is “3 hours” or “2–10 meters (6.6–32.8 feet)”. That is if you ask social media platforms and many newspapers… People are concerned, scared, and frustrated at this point; and everybody’s damn sure about their opinions.

Related stuff: Are you scared of the unknown? This is why.

But is that what the research actually says? Do we really know how long the coronavirus lasts in the air and how far the virus travels to infect? Let’s check!

Do research articles answer how long the coronavirus lasts in the air?

There’s a lot of literature out there about the coronavirus. Still, I think three articles trying to answer our questions have received most of the attention lately. Especially one of these got a massive impact on social media. [Of course, the non-peer reviewed preprint, because, why not, right?] But what did they find?

Study 1: The spray your surrounding experiment (published in the New England Journal of Medicine)

OK, the first one looked into the stability SARS-CoV-2 in aerosols and four different surfaces (plastic, stainless steel, copper, and cardboard). These scientists used a nebulizer (a device that produces small liquid droplets) to spray coronaviruses on different surfaces.

They found that the coronavirus was viable in aerosols for at least 3 hours, with minimal reductions in viral amounts in the air. They also found that plastic and stainless steel maintained stable coronavirus the longest (up to 72 hours), although with a marked reduction in viral amounts.

Study 2: The STAY HEALTHY experiment (also published in the New England Journal of Medicine)

A second publication (not chronologically) tracked the quantity and size of saliva droplets upon speech. The researchers could visualize the released saliva through a laser barrier when one of their lab mates repeated the words “Stay healthy” into a black box. Saliva droplets would light up the next-to-invisible laser barrier ones crossing, thus allowing the team to visualize the droplet cloud as well as the individual droplets.

Turned out uttering the words “Stay healthy,” triggered light flashes, and the louder the scientist exclaimed, “STAY HEALTHY!!”, the higher the resulting peaks would become. This indicated that, while saying the words at different loudness produced droplets of sizes 20–500 microns, loud-speaking released more of the larger particles. 

Obviously, “stay healthy” is not a magic combination of words that elicits these light flashes – any words cause a release in saliva. But, an interesting side note is that the “th” part of “healthy triggered the highest number of flashes. [you already knew you couldn’t trust your lisping friend?]

Anyway, when the team performed the same experiment but “through a slightly damp washcloth over the speaker’s mouth”, the flashlights were close to zero.

Study 3: The saliva cloud simulation experiment (preprint; no peer-review)

Lastly, the one I believe received the most attention in social media was a study that studied how droplets could spread from one person to another during fast movement. These researchers used computer simulations to study droplet spread of people in motion to possibly update the guidelines of 1–2 meters (3.3–6.6 feet).

Related stuff: What is the R0 of the COVID-19 coronavirus and what does it tell you?

They found that people had the most extensive exposure to saliva droplets when running or walking directly behind (in the slipstream of) the leading runner or fast-walker. Depending on the speed of the lead-runner, 5–10 meters (16.4–33.8 feet) behind was enough to avoid exposure to droplets. Running next to a runner or diagonally behind should minimize the exposure.

What we learned from the three studies – the summary

So now, based on these three publications you’ve seen that:

  • The coronavirus can be viable in small aerosols for 3 hours, and plastics and stainless steel maintained the virus for 72 hours.
  • Talking releases saliva droplets of different sizes, and the louder you speak, the larger the particles you release. And, covering your mouth can prevent this release into your immediate surrounding.
  • You increase your risk of receiving saliva droplets when running in the slipstream of another runner. Suggested distance during these activities is 5–10 meters (16.4–33.8 feet) rather than 1–2 meters (3.3–6.6 feet) that apply if you’re standing still.

All three studies suggest that aerosols from breathing and talking – that do not immediately fall to the ground after release – may contribute to the extended spread of SARS-CoV-2 coronavirus. So, I’ll keep wearing my mask while running.

But still, I’m curious…

Wearing green surgical mask balcony How long does the coronavirus last in the air
My green mask and I, going out for a… run?

What you didn’t learn from these studies – the limitations

OK, the information based on these studies seem pretty solid, right? Let’s start tweeting angry messages and cursing all runners and loud-mouths around us for spreading the virus.

But before you go buck-wild on your keyboard, let’s consider a couple of things. I’d argue that these studies, individually, do not answer the question that we were asking before:

How long does the coronavirus last in the air if you release it through breathing or talking? (Assuming that the mouth-breather in question is infected, of course.)

We have to remember that all of these studies were performed in extremely controlled (or simulated) environments that don’t 100% reflect the actual trajectories of the coronavirus.

Viruses in aerosols, but why the random numbers?

A cough or sneeze generates larger particles that presumably falls to the ground rather immediately – hence the 1–2 meters social distancing estimation. The first study tests virus viability and stability in microscopic aerosols and in different conditions. Still, we don’t know why the researchers chose to study the specific sizes of aerosols. Are the selected sizes applicable to real life?  

It’s somewhat clear that the study considers hospital conditions, where healthcare professionals use so-called aerosol-generating procedures. Let’s assume that we do generate and release a significant number of aerosols. I’m still curious about the virus amount contained in each aerosol. Are they realistic and are enough to infect other people (the infectious dose)?

With the information at hand, and although the study analyzes coronavirus viability and stability, this study doesn’t answer our question.

Saliva droplets but no virus

While the last two studies took into account a variety of droplet sizes, these two studies never considered the infectious dose of SARS-CoV-2. That is, although we might get showers of the lead runner’s saliva droplets, we don’t know if that’s the infectious dose. Most of the aerosols reaching us might not contain the virus or contain too little viruses to infect us.  

Related stuff: Learn how they diagnose viruses.

And we cannot blame the studies for these shortcomings. Unfortunately, at this point, we simply do not know the infectious dose, the virus load upon saliva release, or the number of virus particles naturally occurring in aerosols.

The scientific approach – their combined strengths

So no, none of the three studies can answer our question, and we remain clueless as to what extent our breath or talking carry the coronavirus. We still don’t know for how long the virus can stay in the air and especially don’t know if that would be an infectious amount.

Still, that doesn’t mean that these studies are worthless and should be buried somewhere. No, I think that each study contributed to a better understanding of a complicated issue; in their own ways.

You might think, “So these studies are worthless now that I see they have flaws”. Wrong! That’s how research works. Each research group brings its piece to the puzzle, and each piece gets evaluated to see if it fits with the current ones. The individual pieces are incomplete in isolation but play an essential role in our understanding of the big picture.

A jigsaw puzzle. Each piece alone is incomplete, but put together they reveal a more complete picture.

So although we don’t have the exact answer to our question (YET!), they all bring something to the table:

Be extra cautious doing the groceries or touching things because whatever surfaces may contain viable viruses. Keep washing your hands!

Keep social distancing. Whether it is 2 meters (6.6 feet) when standing still or 10 meters (33.8 feet) when running super-fast, it doesn’t hurt to keep the fuck away from other people for a while.

Wear an annoying mask when you’re out in public, especially if you’re strolling around in confined and unventilated spaces. I’ll keep running and training with my beautiful green one; the color distracts me from the lack of oxygen.

Y’all heard this before… no need to repeat. Just #staysafe, OK?

Related stuff: Why does a coronavirus infection treat different age groups differently?

Next time, maybe something about thinking like a scientist or what dogs do while you’re sleeping.

Did you like this post? If you did, would you mind helping us out by sharing it with family and friends? If you didn’t like it, maybe share it with your enemies. It helps us spreading scientific knowledge and thinking.

 
Also, go ahead and comment below. Do you use a mask outdoors? Do you run with a mask on? What color is it?

Links to the studies:

Study 1

Study 2

Study 3

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