Scientists at the University of Bristol have made a significant breakthrough in understanding why airborne viruses lose their infectivity. The research, published in the Journal of the Royal Society Interface, reveals how cleaner air can kill the virus more quickly and why opening a window could be more important in reducing the spread of airborne viruses than previously thought. The research could be instrumental in shaping future mitigation strategies for new viruses.
This is the first study to measure the differences in airborne stability of different variants of SARS-CoV-2 in inhalable particles. The researchers from Bristol’s School of Chemistry have shown that the virus has become less capable of surviving in the air as it has evolved from the original strain through to the delta variant.
Manipulating Gaseous Content of the Air
The team used a next-generation bioaerosol technology instrument called CELEBS (Controlled Electrodynamic Levitation and Extraction of Bioaerosols onto a Substrate) that allowed them to investigate the survival of different SARS-CoV-2 variants in laboratory-generated airborne particles that mimic exhaled aerosol. They examined how environmental factors, such as temperature and humidity, particle composition, and the presence of acidic vapors such as nitric acid, alter virus infectivity over a 40-minute period.
Through manipulating the gaseous content of the air, the team confirmed that the aerostability of the virus is controlled by the alkaline pH of the aerosol droplets containing the virus. They describe how each of the SARS-CoV-2 variants has different stabilities while airborne, and that this stability is correlated with their sensitivities to alkaline pH conditions.
The Role of pH
The high pH of exhaled SARS-CoV-2 virus droplets is likely a major driver of the loss of infectiousness. Therefore, the less acidic the air is, the more alkaline the droplets, and the faster the virus dies. The research suggests that opening a window may be more important than originally thought as fresh air with lower carbon dioxide reduces acid content in the atmosphere and means the virus dies significantly quicker.
The study’s lead author and Senior Research Associate in Bristol’s School of Chemistry, Dr. Allen Haddrell, said, “Our results indicate that the high pH of exhaled aerosol drives the loss of viral infectivity. So, any gas that affects aerosol pH may play a role in how long the virus remains infectious in the air. For example, bleach gives off acidic vapor that may increase SARS-CoV-2 stability in the aerosol phase. Conversely, ammonia which gives off alkaline vapor may have the opposite effect.”
The findings provide valuable insights into why and how aerosolized viruses lose their infectivity, setting the stage for the design of new strategies to mitigate risk. The Director of Bristol Aerosol Research Centre and Professor of Physical Chemistry in the School of Chemistry at the University of Bristol, Jonathan Reid, said, “Our findings broaden our understanding of how environmental factors affect airborne stability of SARS-CoV-2 and other viruses, which will help us design better safety and mitigation strategies to reduce disease transmission. We now intend to explore the role of pH further through studying the role that carbon dioxide has on the risk of SARS-CoV-2 transmission.”
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