Study reveals how SARS-CoV-2 variants lose Infectivity in aerosols: pH and salt content key factors

The recognition of aerosols as the primary transmission route for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for the coronavirus disease 2019 (COVID-19), has led to the implementation of effective prevention measures, including the adoption of masks, air purifiers, social distancing, and ventilation.

In a recent study published in the Journal of the Royal Society Interface, researchers analyze how the decay of SARS-CoV-2 is affected by environmental factors such as temperature, humidity, and particle and gas phase composition.

Study: Differences in airborne stability of SARS-CoV-2 variants of concern is impacted by alkalinity of surrogates of respiratory aerosol. Image Credit: peterschreiber.media / Shutterstock.com Study: Differences in airborne stability of SARS-CoV-2 variants of concern is impacted by alkalinity of surrogates of respiratory aerosol. Image Credit: peterschreiber.media / Shutterstock.com

About the study

Vero E6 cells expressing the angiotensin-converting enzyme 2 (ACE-2) receptor and/or transmembrane protease serine 2 (TMPRSS2) were used in the current study. The CELEBS technique, which is a next-generation bioaerosol technological approach, was used to assess the aero-stability of several SARS-CoV-2 strains including the ancestral Wuhan strain, as well as the Alpha, Beta, and Delta variants.

To this end, a droplet-on-demand dispenser is used to produce a small population of droplets that can be resuspended in growth medium or artificial saliva. An electrode is then applied to induce a net charge onto the droplets, subsequently levitating the droplets into an environment with either low, medium, or high relative humidity (RH) of 40%, 65%, and 90%, respectively. After a specified period of time, the droplets are rapidly extracted and used to treat cells within an incubation period of three to five days.

The researchers then determined the stability of SARS-CoV-2 in these droplet solutions by immunostaining for the infectious virus or determining the median tissue culture infectious dose (TCID50).

Study findings

SARS-CoV-2 Wuhan and Delta strains in aerosol droplets exhibited similar decay properties at low RH; however, the survival of these viral strains when incubated for longer periods at low RH was similar to those observed at a high RH. When present at aerosols, both the Wuhan and Delta strains exhibit measurable differences in their infectivity in as little as five minutes across different RH intensities, which is comparable to other SARS-CoV-2 strains that experience these changes over several hours. Since infectious aerosol droplets can travel several meters in this type of short time period, this observed difference may impact viral transmission in the real world.

The researchers then compared the aero-stability of the different SARS-CoV-2 variants after five minutes of being in the aerosol phase at both low and high RH. To this end, the Delta variant exhibited significantly reduced viral stability in the aerosol phase as compared to other variants.  

Following co-incubation with nitric acid, SARS-CoV-2 variants exposed to a highly acidic environment did not exhibit any changes in their stability in the aerosol form. Notably, since other studies have reported that a high acidic environment inactivates SARS-CoV-2, it is likely that the aerosol has a more basic pH that protects the virus when exposed to an acidic environment.

Comparatively, a more basic environment significantly reduced viral infectivity by up to 90% in just two minutes. This is comparable to ultraviolet (UV) radiation, which takes about eight minutes to neutralize viral infectivity.

Regardless of the RH, the half-life of SARS-CoV-2 continuously increases over time, thus suggesting that the conditions within the droplet become less neutralizing to the virus as time progresses. In the event that an infected person exhales and releases infected aerosols within their surrounding environment, these aerosols will become more acidic over time. This subsequently increases the half-life of SARS-CoV-2 and, as a result, may facilitate viral transmission as a result of its prolonged aero-stability.

Conclusions

Following the emergence of the SARS-CoV-2 Delta variant, many scientists largely attributed the increased transmissibility of this viral strain to immune evasive mutations present in the viral spike protein.

However, in the current study, the researchers observed that the SARS-CoV-2 Delta variant was less aero-stable as compared to the original Wuhan strain when studied in the aerosol phase. This reduced aero-stability may be an evolutionary trade-off, in which the Delta variant utilizes a more effective infection route following the inhalation/deposition event.

Indoor air composition was identified to be a significant contributing factor in the ability of SARS-CoV-2 aerosols to remain infective. In fact, acid vapor appears to prolong the aero-stability and subsequent survival of SARS-CoV-2 variants, thereby contributing to the transmissibility of these variants, particularly in indoor settings.  

An important implication of the current study is to reduce the use of bleach to disinfect areas potentially contaminated with SARS-CoV-2, as hypochlorous acid may inadvertently increase the length of time SARS-CoV-2 remains infectious in the air. Nevertheless, the reaction between SARS-CoV-2 and volatile acids released by cleaning products must be further studied.

Aside from carefully selecting cleaning products for disinfection purposes, the study findings emphasize the importance of social distancing, mask wearing, and well-ventilated areas to minimize exposure to infectious droplets.

Journal reference:
  • Haddrell, A., Otero-Fernandez, M., Oswin, H., et al. (2023). Differences in airborne stability of SARS-CoV-2 variants of concern is impacted by alkalinity of surrogates of respiratory aerosol. Journal of the Royal Society Interface. doi:10.1098/rsif.2023.0062
Bhavana Kunkalikar

Written by

Bhavana Kunkalikar

Bhavana Kunkalikar is a medical writer based in Goa, India. Her academic background is in Pharmaceutical sciences and she holds a Bachelor's degree in Pharmacy. Her educational background allowed her to foster an interest in anatomical and physiological sciences. Her college project work based on ‘The manifestations and causes of sickle cell anemia’ formed the stepping stone to a life-long fascination with human pathophysiology.

Citations

Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Kunkalikar, Bhavana. (2023, June 26). Study reveals how SARS-CoV-2 variants lose Infectivity in aerosols: pH and salt content key factors. News-Medical. Retrieved on July 19, 2024 from https://www.news-medical.net/news/20230626/Study-reveals-how-SARS-CoV-2-variants-lose-Infectivity-in-aerosols-pH-and-salt-content-key-factors.aspx.

  • MLA

    Kunkalikar, Bhavana. "Study reveals how SARS-CoV-2 variants lose Infectivity in aerosols: pH and salt content key factors". News-Medical. 19 July 2024. <https://www.news-medical.net/news/20230626/Study-reveals-how-SARS-CoV-2-variants-lose-Infectivity-in-aerosols-pH-and-salt-content-key-factors.aspx>.

  • Chicago

    Kunkalikar, Bhavana. "Study reveals how SARS-CoV-2 variants lose Infectivity in aerosols: pH and salt content key factors". News-Medical. https://www.news-medical.net/news/20230626/Study-reveals-how-SARS-CoV-2-variants-lose-Infectivity-in-aerosols-pH-and-salt-content-key-factors.aspx. (accessed July 19, 2024).

  • Harvard

    Kunkalikar, Bhavana. 2023. Study reveals how SARS-CoV-2 variants lose Infectivity in aerosols: pH and salt content key factors. News-Medical, viewed 19 July 2024, https://www.news-medical.net/news/20230626/Study-reveals-how-SARS-CoV-2-variants-lose-Infectivity-in-aerosols-pH-and-salt-content-key-factors.aspx.

Comments

  1. Max Sargeson Max Sargeson Australia says:

    "An important implication of the current study is to reduce the use of bleach to disinfect areas potentially contaminated with SARS-CoV-2, as hypochlorous acid may inadvertently increase the length of time SARS-CoV-2 remains infectious in the air. Nevertheless, the reaction between SARS-CoV-2 and volatile acids released by cleaning products must be further studied."

    In the study researchers acidified the airflow with nitric acid in the humidifying bubbler diluted to pH 5, not hypochlorous acid as used in (most) bleaches.

    pH 5 hypochlorous acid (a weak acid) is about 1000 times more concentrated than pH 5 nitric acid (a strong acid), and, while both are strong oxidizers the oxidative effect of the hypochlorous acid in terms of its disinfecting potential by denaturing viral proteins is sure to predominate over the supposedly boosted infectivity due to slightly lower pH, I mean, nobody would use bleach as disinfectant if it didn't.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
Post a new comment
Post

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.

You might also like...
Do SARS-CoV-2 infections cause long-term loss of smell and taste?