Emergence of New Omicron subvariants XBB/XBB.1.5 and BF.7

SARS-CoV-2 Omicron variant emerged in November 2021, since then rapid rates of mutation have replaced the former strains and became the key driver of the pandemic. As of 27 October 2022, the Omicron variant was considered to be the only circulating variant of concern (VOC) by the World Health Organization (WHO) due to its novel mutations. 

In January 2022, the original Omicron strain BA.1 was replaced by BA.2; and then other sub variants BA.3, BA.4, BA.5 and XE have subsequently emerged. On 24 October 2022, the WHO Technical Advisory Group on SARS-CoV-2 Virus Evolution (TAG-VE) concluded that the phenotypes of XBB* and BQ.1* (BA.5 sublineage) were not sufficiently different from other Omicron lineages. However, evidence suggests that the newer Omicron subvariants can re-infect people. 

XBB strain is a recombinant strain of the BA.2.10.1 and BA.2.75 sub lineages which was first documented on 13 August 2022. A recent study concluded that XBB evades neutralizing antibodies in recipients of BNT162b2 or CoronaVac vaccines. 

XBB.1.5, a sublineage of XBB has an additional spike mutation (S486P) in the receptor binding domain and is currently estimated to be of considerable concern due to its rapid spread in December 2022. XBB.1.5 was estimated to have a growth advantage relative to previously circulating lineages in North America and Europe because of the high level of immune escape exhibited by XBB combined with the effect of the spike variant S486P. 

Further, it is also postulated that the enhanced transmissibility of XBB.1.5 is due to its strong ACE2 binding plus antibody evasion. More recently, the monoclonal antibodies Evoshield and Bebtelovimab were shown to have failed to neutralize XBB.1/XBB.1.5. The high transmission potential of these sub variants might however cause difficulties in implementing effective prevention and control measures.
 

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