Omicron more stable than ancestral strain on surfaces, resistant to neutralizing mAbs

The Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is more stable than the ancestral strain on various smooth and porous surfaces and demonstrates marked resistance to neutralizing monoclonal antibodies (mAbs), researchers from the University of Hong Kong (HKU) have reported.

In one study, the researchers showed that Omicron BA.1 was much more stable on stainless steel, polypropylene, glass, tissue paper and printing paper than ancestral SARS-CoV-2. [bioRxiv 2022;doi:10.1101/2022.03.09.483703]

On treated stainless steel, polypropylene and glass surfaces, the Omicron variant could still be recovered on day 7 after incubation at room temperature (21–22°C). In comparison, no infectious ancestral SARS-CoV-2 could be recovered on day 4 post-incubation except on one of three treated glass samples. Infectious viral titres recovered from these treated smooth surfaces were reduced by 98.19 percent, 99.65 percent and 98.83 percent, respectively, on day 7 post-incubation for the Omicron variant, and by 99.91 percent, >99.86 percent and 99.9 percent, respectively, on day 2 post-incubation for ancestral SARS-CoV-2.

On treated tissue paper and printing paper, viable Omicron BA.1 could still be detected after 30 minutes of incubation, while viable ancestral SARS-CoV-2 was no longer recoverable after 30 minutes and 15 minutes of incubation, respectively.

“The extra virus stability [of the Omicron variant] on surfaces may be one possible factor [for its increased transmissibility] and should be taken into consideration when recommending control measures against the infection,” the researchers suggested. “Further studies on the stability of the Omicron variant in droplets and aerosols are warranted.”

In another study, Omicron BA.2 showed marked resistance to 17 of 19 neutralizing mAbs tested, including sotrovimab currently authorized for clinical use. “Overall, 17 of 19 mAbs were either totally inactive or severely impaired in neutralizing BA.2,” reported the researchers from HKU and Columbia University Vagelos College of Physicians and Surgeons in New York, US. [Nature 2022;doi:10.1038/s41586-022-04594-4]

While sotrovimab was found to retain appreciable activity against Omicron BA.1 and BA.1+R346K (ie, BA.1 with R346K mutation, also known as BA.1.1), its neutralizing activity against BA.2 demonstrated a 27-fold decrease to a 50 percent inhibitory concentration of approximately 1 μg/mL.

“Intriguingly but importantly, the S371F mutation appeared to be majorly responsible for the loss in potency of sotrovimab, although this mutation was not observed previously as a marker for clinical resistance to sotrovimab,” the researchers noted. [medRxiv 2021;doi:10.1101/2021.12.18.21267628]

“Bebtelovimab, the most recently authorized mAb, was the only mAb that remained potent in neutralizing all Omicron sublineages,” they pointed out. “Although cilgavimab and its combination with tixagevimab retained activity against BA.2, this mAb combination is authorized for preventive use only.”

The study also showed a substantial loss of neutralizing activity by polyclonal sera from convalescent patients or recipients of mRNA vaccines (with or without a booster shot) against BA.1+R346K and BA.2 relative to wild-type SARS-CoV-2, similar to the decreases already reported for BA.1. Consistent with findings already reported for BA.1, loss of neutralizing activity against BA.1+R346K or BA.2 was less prominent for sera obtained from individuals who received booster vaccination. [Nature 2002;602:676-681; Nature 2002;602;664-670; Nature 2002;602:654-656; Nature 2002;602:671-675]