As the SARS-CoV-2 virus evolves, those characteristics that increase its survival and spread are more likely to become fixed, while traits that don't offer an advantage tend to fade away. For that reason, the virus has become increasingly more transmissible over time, is better able to avoid acquired immunity, and has increased its host range.
During the first year of the pandemic a good deal of attention was placed on cleaning and disinfection (see EID Journal: Aerosol and Surface Distribution of SARS-CoV-2 in Hospital Wards, Wuhan, China), as a way to reduce the spread of the virus.
Fomites, or inanimate objects (doorknobs, desktops, hospital bed rails, even money) were viewed as potential conveyors of the virus, and tests were run to determine how long the virus could remain viable on various surfaces (see EID Journal: Prolonged Infectivity of SARS-CoV-2 in Fomites).
While fomite transmission almost certainly occurred, over time it became pretty obvious that respiratory droplets and aerosols were the primary driver of the pandemic. About a year ago guidance began to de-emphasize the importance of deep cleaning (see CDC Science Brief: SARS-CoV-2 and Surface (Fomite) Transmission).
At least outside of China, which has repeatedly found traces of the virus on imported goods, frozen foods, and even international mail (see China CDC Weekly A Local Cluster of Omicron Variant COVID-19 Likely Caused by Internationally Mailed Document — Beijing Municipality, China, January 2022).
Although early environmental studies showed fairly limited survival times for SARS-COV-2 on most surfaces, we've a new preprint out of the University of Hong Kong that suggests the Omicron variant has become hardier, and can remain viable for much longer on some surfaces.
While this study has yet to be peer-reviewed, it boasts an excellent pedigree, with both Malik Peiris and Leo Poon listed as co-authors. Follow the link to read it in its entirety.
SARS-CoV-2 Omicron variant is more stable than the ancestral strain on various surfacesAlex Chin, Alison Lai, Malik Peiris, Leo Poondoi: https://doi.org/10.1101/2022.03.09.483703This article is a preprint and has not been certified by peer review [what does this mean?].
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Abstract
The Omicron BA.1 SARS-CoV-2 variant of concern spreads quickly around the world and outcompetes other circulating strains. We examined the stability of this SARS-CoV-2 variant on various surfaces and revealed that the Omicron variant is more stable than its ancestral strain on smooth and porous surfaces.
The newly emerged Omicron SARS-CoV-2 variant of concern (VOC) is highly transmissible in humans. It outcompetes other previously known variants and dominates in different geographical locations in recent months (1). Its spike protein has more than 30 mutations compared to the ancestral strain (2).A recent structural study indicates its spike protein is more stable than the ancestral strain (3). This prompts us to hypothesize that Omicron VOC is also more stable on different surfaces. We previously showed that the ancestral SARS-CoV-2 can still be infectious for several days and hours at room temperature on smooth and porous surfaces, respectively (4).Here, we report that Omicron VOC is more stable than the ancestral strain on these surfaces.Previously described ancestral SARS-CoV-2 (PANGO lineage A) and Omicron VOC (PANGO lineage BA.1) were used in this study (5, 6). Their stability on different surfaces were tested using our previously described protocol by us (4, 7). In brief, a 5 l droplet of each virus (10^7 TCID50/ml) was applied on different surfaces with a dimension of 1x1 cm2 . The treated surfaces were incubated at room temperature (21-22C) for different time points as indicated and were then immersed in viral transport medium for 30 min to recover residual infectious virus. The recovered virus was titrated by TCID50 assays using Vero-E6 as described (4, 7).
When compared to the ancestral SARS-CoV-2, the Omicron BA.1 variant was shown to be more stable on all studied surfaces (Table). At 2 days post-incubation, the infectious viral titres of ancestral SARS-CoV-2 recovered from stainless steel, polypropylene sheet and glass reduced by 99.91%, >99.86% and 99.9%, respectively.No infectious ancestral SARS32 CoV-2, except in one out of three treated glass samples, could be recovered on day 4 post incubation.
In contrast, the Omicron variant could still be recovered from these treated surfaces on day 7 post-incubation. Infectious Omicron variant virus recovered from treated stainless steel, polypropylene sheet and glass on day 7 post-incubation reduced by 98.19%, 99.65% and 98.83%, respectively. Thus, the infectious titres of the Omicron variant were not reduced by 3 log10 units on any of these smooth surfaces at our last study time point.The stability of the Omicron variant was also higher than ancestral SARS-CoV-2 on porous surfaces such as facial tissue paper and printing paper. On tissue paper, viable ancestral SARS-CoV-2 was no longer recoverable in 30 min after incubation. However, for the Omicron variant, viable virus could still be detected after a 30-minute incubation and the reduction in titre was less than 3 log10 units (99.34%).On printing paper, the virus titre of ancestral SARS-CoV-2 reduced by 99.68% in 5 minutes and no infectious virus could be detected after a 15-minute incubation. In contrast, the Omicron variant was more stable than the ancestral SARS-CoV-2, with viable Omicron variant virus still recovered from two out of three replicates after a 30-minute incubation.
It isn't clear how much of an impact this increased stability and viability of the Omicron variant is having in the real world, but the authors warn that this study suggests the virus is more likely to be transmitted by the fomite route than its predecessors, and recommend ". . . hand and hygiene and frequent disinfection of common touch surfaces in public areas are highly recommended".
More evidence is needed to account for the increased transmissibility of Omicron variant observed in various community studies. The extra virus stability on surfaces may be one possible factor and should be taken into consideration when recommending control measures against the infection.
Given the enhanced transmissibility of Omicron via the respiratory route, it is difficult to know how much this increased survivability on surfaces is contributing to the spread of the virus, or whether changes to guidelines are justified.
But it does remind us that the SARS-CoV-2 virus is continually evolving, and we need to willing to change our guidelines and assumptions, if and when compelling new data emerges.
