Omikron variant more stable than wild-type variant
After hardly anything was known about SARS-CoV-2 at the beginning of the pandemic, many scientific findings were made in the past years. The stability (also called persistence) of the virus on inanimate surfaces was also researched extensively, since this allows to draw conclusions about the risk of transmission through e.g. door handles or light switches. However, the mutability of the virus regularly reshuffles the cards, as the variants can differ in their stability.
Already in April 2020, van Doremalen et al. [1] have shown that the stability on surfaces depends not only on the virus itself but also on the surface material. The researcher compared the wild-type variant of SARS-CoV-2 with SARS-CoV-1, which circulated mainly in Asia in 2002/2003, and concluded that both are similarly stable. However, the stability on plastic and stainless steel was significantly increases compared to copper or cardboard surfaces. Infectious virus particles have been found on plastic and steel even after 72 hours, while no intact viruses were found on copper after 4 hours (SARS-CoV-2) or 8 hours (SARS-CoV-1), respectively [1].
A recent study by Hirose et al. compared the stability of different SARS-CoV-2 variants on plastic and skin [2]. The result: all analysed variants (Wuhan, Alpha, Beta, Gamm, Delta, Omikron BA-1, and BA.2) remained intact on plastic surfaces much longer than on skin. Furthermore, the Omikron variants were significantly more stable than for example the Wuhan or Gamma variants. The shortest median survival times were 8.6 hours (skin) and 56 hours (plastic) for the Wuhan variant, while the longest survival times were 22.5 hours (skin) and 199.7 hours (plastic) for Omikron BA.2 [2]. The good news is that all variants could be sufficiently inactivated by standard alcohol-based disinfectants with virucidal activity against enveloped viruses [2]. Even though the currently predominant Omikron variants BA.4 and BA.5 were not yet included in the study, similar efficacy can be assumed based on the viral envelope.
When it comes to statements about the stability of the virus, attention must be paid to the detection methodology. A research team lead by Professor Johannes Knobloch (University Medical Center Hamburg-Eppendorf) recently investigated the extent to which CT values obtained from surface samples by quantitative real-time PCR reflect the risk of infection [3]. It was found that these values alone do not indicate whether infectious SARS-CoV-2 viruses are present; indeed, PCR was also possible with the residual RNA of inactive virus particles. While PCR was positive in several samples from the ICU environment, the researchers were unable to obtain infectious viruses from these samples [3].
It must not be inferred from the results that SARS-CoV-2 contaminated surface do not pose any risk of infection. Especially in sensitive areas, surface disinfection remains an important component of infection prevention.Sources:
