Coronavirus Loses Most Infectiousness in Air in 10 Minutes

  • A study suggests that coronavirus particles can’t survive for very long while suspended in the air.
  • In the lab, they lost much of their capacity to infect within about 10 mins, the study found.
  • Omicron, which was not included in the study, could behave differently, experts previously said.

The coronavirus quickly lost its ability to infect human cells after it was released in tiny droplets suspended in the air, a lab study found.

Researchers observed the particles drying up in the environment outside the body, hampering their ability to infect cells.

The study, published as a pre-print on Monday that has not been independently reviewed, provides clues as to how aerosols that are released when talking and sneezing contribute to infection.

The work took place before the Omicron variant spread widely, so it is unclear whether its results would also apply to the now-dominant variant of the virus.

“People have been focused on poorly ventilated spaces and thinking about airborne transmission over meters or across a room,” Prof Jonathan Reid, the study’s lead author, told The Guardian.

“I’m not saying that doesn’t happen. But I think still the greatest risk of exposure is when you’re close to someone,”  he said.

The findings suggest that the risk of getting infected by particles suspended in the air depends not only on how many there are floating around, but also on their “freshness,” Denis Doorly, an expert in fluid mechanics at Imperial College London who was not involved in the research, told Insider in an email.

Doorly specified, however, that this does not take away from the importance of ventilation as “infectivity does not diminish to zero even after long times.”

It is not clear whether the phenomenon might be different if moved from a lab setting to the real world. 

Scientists at the University of Bristol, UK, designed a machine that can keep the airborne droplets in levitation.

The scientists can change the temperature and humidity in the chamber to mimic the conditions in the outside air. They can put the droplets containing the virus on human cells in a Petri dish. If the virus grows there, it’s still alive. 

In this setting, the study found that within about 5 seconds of being released in 40% humidity air — which is similar to the settings in an office, or a bar — half of the virus was no longer unable to infect human cells, as seen in red in the figure below. 

A figure from the study shows infectivity of the coronavirus over time.

Lab results show short-term decay of the COVID-19 coronavirus in the air in a 40% humidity setting (red) and 90% humidity setting (green)

eg: Oswin, H. et al. 2021, medRXiv

The ability of the virus to infect cells further dwindled over time.

Within ten minutes, the “majority” the virus was inactivated, the authors said in the study. Within 20 minutes, about 90% of the virus particles were inactive, per the study.

Humidity was more important than temperature in preserving the viruses’ ability to survive in the air, per the study.

In higher humidity, about the level seen in a shower or steam room, the virus stayed stable much longer, as pictured in green above.

Half of the particles were still able to infect within the first minutes of being suspended, the results said. But over time the particles decayed, losing most of their ability to infect within 20 mins, like at lower humidity levels. 

It is not clear how reproducible these results are to real-life settings where there are other factors at play, like ventilation, size of the room, and how much virus an infected person is shedding.

It is also possible, for instance, that 10% of the original viral load is enough to cause an infection in someone across the room, which would mean the virus is dangerous even after waiting for some time.

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