In a recent study, Japanese researchers report that the new variant of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), Omicron, has greater environmental stability than previous variants.
Study: Differences in environmental stability among SARS-CoV-2 variants Worrying: Omicron has higher stability. Suitable for Ztudio/Shutterstock
The study, published on preprint server bioRxiv*, compared the SARS-CoV-2 Wuhan strain and variants of concern (VOCs) – alpha, beta, delta and omicron variants – for their survivability and infectivity.
Using engineered human skin models and plastic substrates, researchers assessed the variants’ environmental stability
Understanding the pathogenesis of SARS-CoV-2 and its stability in the environment is critical to containing the ongoing pandemic that has caused debilitating damage around the world.
Since the first days, the SARS-CoV-2 progenitor virus has shown high transmissibility. With the emergence of many variants, the virus has gained greater transmissibility, as evidenced by the number of cases of infection despite vaccines and lockdowns around the world.
Several factors are attributed to the increased infectivity and transmissibility of SARS-CoV-2, such as and increased environmental stability.
However, no study to date directly compares the stability of the ancestral virus and its variants of concern in detail and reports on their environmental stability. There are previous studies that have reported that Alpha (Pango line: B.1.1.7) and Beta (Pango line: B.1.351) have similar stability. Some studies have compared the stability of SARS-CoV-2 to that of severe acute respiratory syndrome coronavirus (SARS-CoV-1) and influenza virus.
The present study accurately assessed the differences in virus stability of Wuhan strain (Pango lineage: A) and all VOCs including Omicron (Pango lineage: B.1.1.529) and Delta (Pango lineage: B.1.617.2 ). Variant. They also analyzed the disinfection effectiveness between the Wuhan strain and all VOCs.
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 researchers used VeroE6/TMPRSS2 cells to cultivate the viruses.
Researchers evaluated virus stability on plastic (Styrofoam sheet) and human skin surfaces. Using human skin obtained from forensic autopsy specimens, the researchers developed an ex vivo model.
After applying the virus to the plastic/skin surface, they tested the viability of the virus. They evaluated the stability of different viruses on the surface of the human skin model and also found the effectiveness of different disinfectants against viruses on human skin. The alcohol-based disinfectants ethanol and isopropanol were used in the study.
The researchers defined 100.5 TCID50 as the detection limit for the titer of the virus remaining on the surface and the time until the virus was no longer detectable on the surface as the survival time.
On the plastic surface, the researchers analyzed the survival times of Wuhan strain, Alpha variant, Beta variant, Gamma variant, Delta variant and Omicron variant as 56.0 h, 191.3 h, 156, 6 h, 59.3 h, 114.0 h and 193.5 h, respectively
While on the human skin surface, they analyzed the survival times of the Wuhan strain, alpha variant, beta variant, gamma variant, delta variant and omicron variant with 8.6 h, 19, 6 hrs, 19.1 hrs, 11.0 hrs, 16.8 hrs and 21.1 hrs; with the Omicron variant having the longest survival time. The researchers reported that the half-life trended in the same way as the survival time.
The disinfectants were effective against all viruses within 15 seconds. However, the VOCs have been a bit more resilient than the Wuhan tribe. On human skin, an ex vivo evaluation showed complete inactivation of all viruses within 15 seconds of exposure to 35% ethanol. Therefore, the researchers strongly recommend continuing the current protocol of hand hygiene practices for infection control, as recommended by the World Health Organization.
Thus, this study showed that the VOCs on plastic and skin surfaces showed survival times more than two times longer than that of the Wuhan strain and remained infectious on the skin surfaces for more than 16 hours.
limitations of the study
The study does not go into the reasons for the observed higher environmental stability of the variants.
Further research using recombinant viruses could identify the factors behind this, the researchers observed. Importantly, the survival time and half-life assessed in this study depend on the external environment and body fluid composition.
In this study, the virus was ultracentrifuged and dispersed in PBS (phosphate buffered saline) solvent. Therefore, it can change according to the number of variables in the environment.
In addition, the relationship between surface viral load and transmission risk is unclear.
Therefore, it might make sense to interpret the survival time value in this study as a reference value,” the researchers state in the paper.
Information on the stability of the virus and its variants responsible for the ongoing pandemic is critical for infection control and containment. This study examined the environmental stability of SARS-CoV-2 and its variants of concern. It was found that the Omicron variant has the highest environmental stability among the VOCs; suggesting how Omicron quickly replaced the Delta variant and spread wildly across the globe.
In addition, these results will significantly help elucidate the mechanism of VOC spread by adding genetic analysis, the researchers conclude.
bioRxiv publishes preliminary scientific reports that have not been peer-reviewed and therefore should not be relied upon as conclusive, to guide clinical practice/health-related behavior, or treated as established information.