In a recent study published in bioRxiv* Preprint server Researchers are conducting large-scale multiscale investigations to explore the virological characteristics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron XBB subspecies, XBB.1.16.

Stady: Viral characteristics of the SARS-CoV-2 variant Omicron XBB.1.16. Image credit: Limbitech/Shutterstock.com

*Important note: bioRxiv It publishes preliminary scientific reports that have not been peer-reviewed and therefore should not be considered conclusive, directing clinical practice/health-related behaviour, or treated as hard information.


The SARS-CoV-2 variant XBB.1.16 is associated with a 1.27- and 1.17-fold greater effective reproduction number (RH) in comparison with sub-variants XBB.1 and XBB.1.5, respectively, indicating the ability of this new Omicron variant to spread rapidly.

As a result of this increased transmission, the World Health Organization (WHO) began monitoring XBB.1.16 on March 30, 2023, after it was detected in several countries, including India. Earlier, SARS-CoV-2 Omicron XBB sub-variants with an F486P substitution in the spike (S) protein, which include XBB.1.5 and XBB.1.9, were widespread throughout the world.


The present analyzes showed that compared with previous mutant strains, XBB.1.16 had two S substitutions, including E180V and T478R in its N-terminal domain (NTD) and receptor-binding domain (RBD), respectively. Moreover, the dissociation constant (KDr) of XBB.1.16 RBD of the host receptor angiotensin converting enzyme 2 (ACE2) was 2.4-fold higher than that of XBB.1.5; However, KDr The values ​​were significantly weaker than those for XBB.1, reflecting the binding affinities of this new variant.

Pseudovirus assays showed that the infectivity of XBB.1.16 was comparable to XBB.1 but unlike XBB.1.5, in which the infectivity was higher than that of the parental XBB.1 mutant. Note that the S:T478R and S:E180V substitution mutations have a significant effect on the infection of this viral variant. Whereas the S:T478R mutation increased the infectivity of XBB.1.16, the S:E180V substitution significantly reduced the viral infectivity.

It is possible that XBB.1.16 acquired these two S protein mutations simultaneously as an evolutionary strategy. This behavior has been previously observed in other sub-Omicron variants, including BA.5 and XBB.1. Indeed, XBB.1.16 follows the evolutionary path of the previously appeared sub-Omicron variants.

With regard to sensitivity to serum, neutralization assays showed that XBB.1.16 was highly resistant to sera from individuals infected with Omicron BA.2/BA.5, and 18- and 37-fold more resistant than Omicron B.1.1/B.1.1. However, the sensitivity of this variant to the serum of convalescent hamsters infected with XBB.1 was similar to the XBB.1/XBB.1.5 mutants.

XBB.1.16 was highly resistant to all six clinically available SARS-CoV-2 monoclonal antibodies. Only sotrofimab showed antiviral activity against XBB.1.16; However, this effect was weak. Finally, antigenic mapping showed that the XBB.1.16 antigen has a proximal antigen of XBB.1; However, this property is significantly different from that associated with XBB.1.5.


Overall, the current extensive exploratory analyzes revealed that the SARS-CoV-2 Omicron XBB.1.16 variant has enormous potential to spread and infect people worldwide to a greater extent than the XBB.1 and XBB.1.5 sub-variants. Moreover, XBB.1.16 shows higher immune evasion capabilities similar to those of XBB.1 and XBB.1.5.

The authors concluded that XBB.1.16 has a higher fitness and growth advantage due to the presence of different antigens than XBB.1.5. Furthermore, mutations in non-S SARS-CoV-2 proteins are also likely to contribute to improved fitness.

*Important note: bioRxiv It publishes preliminary scientific reports that have not been peer-reviewed and therefore should not be considered conclusive, directing clinical practice/health-related behaviour, or treated as hard information.

written by

Neha Mathur

Neha is a digital marketing professional based in Gurugram, India. She completed her Masters degree from the University of Rajasthan with a major in Biotechnology in the year 2008. She has experience in preclinical research as part of her research project in the Department of Toxicology at the prestigious Central Drug Research Institute (CDRI), Lucknow, India. She also holds a certification in C++ Programming.


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