How Long Is the Coronavirus Infectious When It’s in the Air?

6 月 10, 2022World News

As the fast-moving Omicron variant of the coronavirus continues to sweep across the United States, scientists are learning more about the virus and how it spreads.

A new study from the University of Bristol in England determined that the novel coronavirus, SARS-CoV-2, loses most of its ability to transmit from one person to another 20 minutes after becoming airborne.

At this point, the virus was found to lose 90 percent of its potency.

“A decrease in infectivity to approximately 10 percent of the starting value was observable for SARS-CoV-2 over 20 minutes, with a large proportion of the loss occurring within the first 5 minutes after aerosolisation,” scientists wrote in the paper, which has not yet been published or peer-reviewed.

The research suggests the coronavirus does not survive for long outside of the human host’s body and loses its infectiousness rather quickly.

How does COVID-19 spread?

So, how can we use this information to evaluate our risk in different situations?

First, it’s important to understand how COVID-19 spreads.

The primary way the coronavirus is transmitted from person to person is through respiratory droplets.

“Those are large water droplets that are expelled when people cough or sneeze, and they have virus inside of them,” said Taylor Nelson, DO, an infectious disease specialist at University of Missouri Health Care.

When someone is in close contact with a person with an infection who expels these droplets, they can contract an infection if those droplets reach their eyes, mouth, or nose.

How long is the coronavirus infectious when it’s in the air?

How long the coronavirus is infectious when it’s in the air is a question scientists have been trying to pinpoint since the beginning of the pandemic.

Previous studies relied on spraying virus into rotating sealed chambers to create an aerosolized environment. Using this technique, researchers determined that the virus could still be detected for 3 hours. However, such experiments do not accurately replicate what happens when a person with an infection exhales.

For the new study, scientists developed a device that uses an electric field to levitate tiny, virus-containing droplets. While controlling for temperature, humidity, and UV light intensity, researchers tested the infectiousness at various lengths of time from 5 seconds to 20 minutes.

“That’s far more representative of a close contact exposure where an infected person next to you talks or coughs,” explained Herek Clack, PhD, associate professor of civil and environmental engineering at the University of Michigan. “That control of precision is something that had not been available using established techniques prior to this.”

The study found that in air with 50 percent humidity — similar to what would be circulating in large buildings or offices — there is “a near instant loss of infectivity in 50–60% of the virus.”

At 90 percent humidity (think a shower or steam room), the virus remained stable for longer and sustained its infectiousness for 2 minutes. There was a gradual decline in infectiousness after this, reaching 10 percent after 10 minutes.

Evaluating your risk of exposure

The results of the study emphasize the importance of physical distancing to prevent infection.

“Close proximity for a prolonged duration is going to be still the highest risk of transmission from another person, especially someone who’s coughing or yelling,” Nelson said.

When it comes to evaluating your risk in different situations, experts say there are a number of factors to weigh.

“If you’re in a confined space with people in very close contact for a long time, that’s going to be the highest risk, especially if you’re not wearing a mask,” Nelson said, “versus if you’re walking through Walmart for 5 minutes and not really close to someone, generally speaking, that’s lower risk.”

Clack likens exposure risk to being around someone who is smoking.

“If I’m walking behind or close to someone, I think to myself, based on where they are and my relationship to them, would I expect to smell the smoke of their cigar or cigarette?” he said. “If so, take a step to the side, slow down, and then allow yourself to be a little further behind them to avoid walking through that plume of smoke.”

When it comes to dining at a restaurant indoors, the new research demonstrates that, generally speaking, the greatest risk of exposure would come from the people you’re sitting at a table with or those closest to you, rather than someone across the restaurant.

However, Clack cautions this may not always be the case depending on ventilation.

“If somehow the configuration is that in this restaurant, the ventilation system is blowing infectious aerosols from an infected person over to you, then I would not say the risk is lower than anything else,” he said.

Vaccination is still the best to protect yourself from COVID-19

Ultimately, the best way to protect yourself from COVID-19 is to get vaccinated and boosted.

“Right now, we’re dealing with a really transmissible, really infections variant,” Nelson said. “Luckily, in a lot of people, it seems to be a relatively mild infection if they’re vaccinated and boosted. So that’s really the best way to protect yourself from severe infection that would require hospitalization or worse.”

Additionally, the tried-and-true measures we’ve come to rely on throughout the pandemic still hold up.

“All of the things that we’ve been talking about from day one, so masks, social distancing, good ventilation systems,” she said. “If you’re going to meet up with others, meet up outdoors. It’s a combination of all these things that will help to protect you.”

 

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