Covid loses 90 per cent of infectiousness 5 minutes after becoming airborne, study finds

·2-min read
Stock image  (PA Archive)
Stock image (PA Archive)

Covid-19 loses 90 per cent of its infectiousness within five minutes of becoming airborne, research found.

Researchers at the University of Bristol used special equipment to test how long Covid could survive in tiny airborne particles under a range of heat, humidity and light conditions.

The study, which has not yet been peer-reviewed, is believed to be the world’s first simulation of how the virus survives in exhaled air.

The research, first reported by the Guardian, found the small viral particles become dramatically less effective and eventually dry out after leaving the carbon dioxide-rich conditions of the lungs.

However, the speed at which the particles dry out largely depends on the humidity of the surrounding air.

At below 50 per cent humidity – similar to the air found in an office – the virus lost half of its infectiousness within 10 seconds of becoming airborne.

At 90 per cent humidity – similar to a steam room or shower – around 52 per cent of particles remain infectious after five minutes.

This figure dropped to around 10 per cent after 20 minutes.

Professor Jonathan Reid, lead author of the study, told the publication: “People have been focused on poorly ventilated spaces and thinking about airborne transmission over metres or across a room. 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 added: ““When you move further away, not only is the aerosol diluted down, there’s also less infectious virus because the virus has lost infectivity [as a result of time].”

The temperature of the air had no impact on viral infectivity, according to the study.

This was a sharp contrast to the commonly held belief that viral transmission rates drop during warm weather.

“It means that if I’m meeting friends for lunch in a pub today, the primary [risk] is likely to be me transmitting it to my friends, or my friends transmitting it to me, rather than it being transmitted from someone on the other side of the room,” said Reid.

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