Japanese researchers recently reported that Omicron (the new variant of the severe acute respiratory disorder coronavirus 2 or SARS-CoV-22) has higher environmental stability compared to previous variants.
Study: Environmental stability differences among SARS CoV-2 variants of concern. Fit Ztudio/Shutterstock
The study has been posted on the preprint web server bioRxiv*We compared the SARS CoV-2 Wuhan strain with variants of concern (VOCs – Alpha, Beta and Delta) to determine their viability and infectivity.
Researchers evaluated the environmental stability using constructed human skin models and plastic substrates
Introduction
Understanding the origins of the SARS-CoV-2 virus and its stability in the environment are critical to reducing the debilitating effects that continue to plague the world.
Since its inception, the transmissibility rate of the SARS CoV-2 ancestral virus was high. The virus has become more transmissible with the emergence of new variants. This is evident in the increase in infection cases despite vaccinations and lockdowns around the world.
The increased infectivity of the SARS-2 virus can be attributed to several factors, including increased viral load from infected people, prolonged viral shedding, decreased viral load necessary to establish infection, changes at the infection target site, and greater environmental stability.
To date, however, there has not been a study that directly compares the stability and environmental stability of the ancestral virus with its variants of concern. Previous studies have shown that the stability of the Alpha (Pango Lineage: B.1.1.7) as well as Beta (Pango Lineage: B.1.351), are similar. Some studies have compared SARS-CoV-2 stability with that of severe acute respiratory syndrome coronavirus, (SARS-CoV-1) as well as the influenza virus.
The present study assessed the differences in viral stability among the Wuhan strain (Pangolineage: A), all VOCs (including the Omicron lineage of Pango: B.1.1.529), and the Delta lineage of Pango: B.1.617.2). They also evaluated the disinfection efficacy of the Wuhan strain and all VOCs.
The study
All viruses ( Wuhan strain (Pango lineage: A, hCoV-19/Japan/TY/WK-521/2019), Alpha variant (Pango lineage: B.1.1.7, hCoV-19/Japan/QK002/2020), Beta variant (Pango lineage: B.1.351, hCoV-19/Japan/TY8-612/2021), Gamma variant (Pango lineage: P.1, hCoV-19/Japan/TY7-501/2021), Delta variant (Pango lineage: B.1.617.2, hCoV-19/Japan/TY11-927/2021), and Omicron variant (Pango lineage: B.1.1.529, hCoV-19/Japan/TY38-873/2021)) in the study were provided by the National Institute of Infectious Diseases (Tokyo, Japan). The VeroE6/TMPRSS2 cells were used by the researchers to cultivate the viruses.
Researchers evaluated the virus stability of plastic (polystyrene-plate) and human skin surface surfaces. The researchers created an algorithm using the human skin from forensic autopsy specimens. ex vivo model.
They tested the virus’s viability on the plastic/skin surfaces after applying it. They also evaluated the stability and effectiveness of different viruses on human skin models. The study used ethanol and isopropanol, which are both alcohol-based disinfectants.
Researchers defined 100.5 TCID50 as the detection limit for virus remaining on the surface. Survival time is the time that the virus was not detected.
Researchers compared the survival times of the Wuhan strains, Alpha variants, Beta variants, Gamma variants, Delta variants, and Omicron varieties on the plastic surface to determine that they were 56.0, 191.3, 156.6, 59.5, and 56.0 hours, respectively.
They measured the survival times of the Wuhan strains, Alpha variants, Beta variants, Gamma variations, Delta variants, and Omicron varieties on human skin. The results were 8.6 h to 19.6 h to 19.1 h and 11.0 h respectively. Omicron had the longest survival time. Researchers reported that the half-life values had the exact same tendency as the survival times.
All viruses were killed by disinfectants within 15 seconds. However, VOCs were slightly more resistant to the Wuhan strain. An ophthalmologist can see the VOCs on human skin. ex vivo All viruses were inactivated by 35% ethanol exposure within 15 minutes. Researchers recommend that hand hygiene practices be continued as recommended by the World Health Organization.
This study demonstrated that VOCs had a greater survival rate on plastic and skin surfaces than the Wuhan strain, and remained infective for longer than 16 hours.
Limitations of this study
The reasons for the observed higher levels of environmental stability in the variants are not addressed in the study.
The researchers suggested that further research using the recombinant viral technology could help to identify the causes. Importantly, the external environment and composition of the body fluid play a significant role in determining the survival time and half life.
The virus was ultracentrifuged in phosphate buffer saline (PBS) solvent. It is therefore subject to change depending on the environmental variables.
It is also unclear what the relationship between virus load and risk of transmission is.
Therefore, it might be reasonable to interpret the value of survival time in this study as a reference value,” observed the researchers in the paper.
Conclusion
For infection control and mitigation, it is vital to have information about the stability of the virus as well as its variants. This study examined the environmental stability of SARS-CoV-2, as well as its variants. It was found that the Omicron variant had the highest environmental stability of all VOCs. This is a sign of how Omicron rapidly replaced the Delta variant, and has quickly spread around the globe.
These findings will also help to understand the mechanism of VOC spread when combined with genetic analysis, researchers conclude.
*Important notice
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.