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COVID-19 infectivity drops 90%, 20 minutes in the air: preprint

A new pre-print study has offered preliminary evidence suggesting that the virus that causes COVID-19 loses most of its infectivity after 20 minutes in the air.

The not yet peer-reviewed study in the UK measured the stability of SARS-CoV-2 in aerosol droplets between five seconds and 20 minutes.

After 20 minutes, the researchers say that the infectivity of SARS-CoV-2 has fallen to about 10% from where it started, with much of that loss occurring within the first five minutes after aerosolization.

The article is a pre-print and has not been peer reviewed, meaning it has not been reviewed by the medical community for any errors or inaccuracies.

Researchers say the data suggests that dry air may help limit overall exposure to SARS-CoV-2, although more research is needed to confirm this, as well as the possible effect of pH and blood levels. CO2.

The study also based most of its measurements on versions of SARS-CoV-2 isolated at the start of the pandemic, including Alpha. However, he found no significant difference between the three variants that were used.

“While the current general consensus is that the half-life of SARS-CoV-2 in the aerosol phase is between 1 and 2 hours or more, we report a rapid initial decline in infectivity within seconds to a few minutes after aerosol generation. “, write the authors of the study.

“Under all conditions measured, the majority of SARS-CoV-2 is inactivated within 10 minutes of aerosolization. More research is needed to determine how long the remaining fraction persists and how this may depend on the viral load in the aerosol.

Transmission of droplets containing SARS-CoV-2 has led to continued discussions of ventilation, masking and social distancing, with reports varying on how long the virus can remain aerosolized or airborne. .

The survival time of SARS-CoV-2 has been examined since the early days of the pandemic.

The Public Health Agency of Canada says SARS-CoV-2 is spread from one infected person to others through respiratory droplets, the size of which can range from large droplets that fall to the ground in seconds or minutes to small, sometimes called aerosols, that linger in the air especially indoors.

Information released by UK Research and Innovation in May 2020 indicates that SARS-CoV-2, like many respiratory viruses, is spread primarily between people through small droplets released from the nose or mouth of an infected person.

He said at the time that the half-life, or the time it takes for 50% of the virus to be no longer infectious, in droplet aerosols was just over an hour, with some surviving for three hours or so. more.

By the spring of 2021, scientists and doctors had increasingly come to the conclusion that aerosols were the main mode of transmission of SARS-CoV-2.

The latest UK study used a technique called CELEBS, or controlled electrodynamic levitation and extraction of bioaerosols from a substrate, which involves suspending particles containing the virus under controlled conditions. The particles are then spread on a cell culture.

The researchers found that the infectivity of SARS-CoV-2 at low relative humidity, or 40 percent, dropped almost immediately to an average of 54 percent in five seconds.

This was followed by a period of relative stability, diminishing to an average of 19 percent after five minutes.

Under conditions of high relative humidity of 90 percent, infectivity after aerosolization fell more gradually to 48 percent during the first five minutes.

In both scenarios, infectivity appeared to peak after 10 minutes before reaching similar points after 20 minutes.

The researchers say the data is consistent with the view that the virus mainly spreads over short distances.

“The rapid loss of infectivity demonstrated in these measurements provides an alternative explanation for a short transmission distance, with rapid airborne losses of viral infectivity making transmission less likely as the distance from the particle source increases. , even though the particles that contain the virus are small and able to travel long distances, ”the study said.

Regarding CO2, researchers say high levels are a sign that a space is densely occupied and poorly ventilated, possibly creating conditions where SARS-CoV-2 is more stable in the air. They suggest that CO2 monitors could be useful in assessing the relative risk of an indoor environment.