The study team analyzed the differences in viral environmental stability between the SARS-CoV-2 Wuhan strain and all variants of concern (VOCs). On plastic and skin surfaces, Alpha, Beta, Delta, and Omicron variants exhibited more than two-fold longer survival than the Wuhan strain and maintained infectivity for more than 16 h on skin surfaces.
The high environmental stability of these VOCs could increase the risk of contact transmission and contribute to their spread.
However, when compared to all other new variants such as the Alpha, Beta, Delta and Gamma variants, the Omicron exhibited longer survival time on plastic and skin surfaces.
The study findings were published on a preprint server and are currently being peer reviewed. https://www.biorxiv.org/content/10.1101/2022.01.18.476607v1
The virus titers remaining on the plastic or human skin surfaces were measured over time (Supplementary Figure S1), and the survival time and half-life were calculated from these titer values by regression analysis (Supplementary Figure S2).
In the plastic surface analysis, survival times of the Wuhan strain, Alpha variant, Beta variant, Gamma variant, Delta variant, and Omicron variant were 56.0 h (95% confidence interval [CI], 39.0–76.7 h), 191.3 h (95% CI, 152.5–232.1 h), 156.6 h (95% CI, 122.7–192.9 h), 59.3 h (95% CI, 43.9–77.7 h), 114.0 h (95% CI, 91.3–139.1 h), and 193.5 h (95% CI, 153.1–236.2 h), respectively (Figure 1A and Supplementary Table S1). In the human skin surface analysis, survival times of the Wuhan strain, Alpha variant, Beta variant, Gamma variant, Delta variant, and Omicron variant were 8.6 h (95% CI, 6.5–10.9 h), 19.6 h (95% CI, 14.8–25.3 h), 19.1 h (95% CI, 13.9–25.3 h), 11.0 h (95% CI, 8.1–14.7 h), 16.8 h (95% CI, 13.1–21.1 h), and 21.1 h (95% CI, 15.8–27.6 h), respectively (Figure 1B and Supplementary Table S1). Alpha, Beta, Delta, and Omicron variants had significantly longer survival times than the Wuhan strain, and the Omicron variant had the longest survival time. Furthermore, the half-life showed the same tendency as the survival time (Figure 1C and 1D and Supplementary Table S2).
The Omicron variant is currently a major concern owing to the rapidly increasing number of infected patients worldwide. The shift in the target site of infection from the lower respiratory tract to the upper respiratory tract and the escape from neutralizing antibodies might be potential factors for the spread of the Omicron variant (1–5).
This study showed that the Omicron variant also has the highest environmental stability among VOCs, which suggests that this high stability might also be one of the factors that have allowed the Omicron variant to replace the Delta variant and spread rapidly.
Although Alpha, Beta, Delta, and Omicron variants showed a slight increase in ethanol resistance in response to increased environmental stability, all VOCs on the skin surface were completely inactivated by 15 s exposure to 35% EA.
Therefore, it is highly recommended that current infection control (hand hygiene) practices use disinfectants with appropriate EA concentrations (>52 w/w% or >60 v/v%), as proposed by the World Health Organization (16, 17).