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Levitating drops. Each of these droplets has a single SARS-CoV-2 virus particle. The droplets look like lines because they are moving rapidly in an electric field. Credit: University of Bristol

Researchers at the University of Bristol have discovered important insights into why airborne viruses lose their ability to infect. The results, which were published in Journal of the Royal Society Interface today, reveal how cleaner air kills the virus significantly faster and why opening windows may be more important than originally thought. The research could shape strategies to reduce new viruses in the future.

In the first study to measure differences in the airborne stability of different variants of SARS-CoV-2 in inhaled particles, researchers from Bristol’s School of Chemistry show that the virus has become unable to survive in the air as it has evolved from the original strain through to the delta variant.

Dr. Allen Haddrell, lead author of the study and senior research fellow at Bristol’s School of Chemistry, explained: “Aerosols exhaled when infected individuals breathe, talk or cough can transmit viruses – but how and why viruses lose their infectivity once they are in circulation . around these airborne particles there has been much controversy.”

To carry out the study, the team used a next-generation biospray technology device they developed called CELEBS (Controlled Electrodynamic Emission and Extraction of Biospray on a Substrate), which allowed them to study the survival of different SARS-CoV-2 variants in the laboratory. airborne particles that mimic an exhaled aerosol. They looked at how environmental factors, such as temperature and humidity, particle composition and the presence of acidic vapors such as nitric acid, change the infectivity of the virus over a 40-minute period.

By controlling the gaseous content of the air, the team confirmed that the air resistance of the virus is controlled by the alkaline pH of the aerosol droplets containing the virus. Importantly, they describe how each of the SARS-CoV-2 variants has different stability while in the air and that this stability is related to their sensitivity to alkaline pH conditions.

The high pH of exhaled SARS-CoV-2 virus droplets is likely a major driver of loss of infectiousness, so the less acid in the air, the more alkaline the droplet is, the faster the virus dies. Opening a window may be more important than originally thought as fresh air with lower carbon dioxide, reduces the acid content of the atmosphere and means the virus dies significantly faster.

Dr. Haddrell added: “Our results suggest that the high pH of exhaled aerosols causes the viral infection to be lost. So any gas that affects the pH of aerosols can play a role in how long the virus remains infectious in the air. For example, bleach . emits acidic vapors that can increase the stability of SARS-CoV-2 in aerosols. Conversely, ammonia, which emits alkaline vapors, can have the opposite effect.”

The results provide valuable insight into why and how aerosolized viruses lose their infectivity, and lay the groundwork for the design of new strategies to reduce risk.

Jonathan Reid, director of the Bristol Aerosol Research Center and professor of physical chemistry at the University of Bristol’s Department of Chemistry, and one of the corresponding authors, said: “There are numerous factors that influence the transmission of viruses in the air, and these are often confounded with physical and environmental factors. parameters that can affect the longevity of a virus in an aerosol such as temperature, humidity, air movement and UV light.

“Our findings broaden our understanding of how environmental factors affect the stability of SARS-CoV-2 and other airborne viruses, which will help us design better safety and countermeasures to reduce disease transmission. We now plan to investigate the role of pH further by investigating the role of carbon dioxide in the risk of SARS-CoV-2 infection.”

More information:
Differences in airborne stability of SARS-CoV-2 variants of concern are affected by the alkalinity of the surrogate respiratory spray, Journal of the Royal Society Interface (2023). DOI: 10.1098/rsif.2023.0062. … .1098/rsif.2023.0062

Diary information:
Journal of the Royal Society Interface

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