Inactivated SARS-CoV-2 Variant Omicron, Lineage BA.5.5 (USA/NY-Wadsworth-22023478-01/2022)

The SARS-CoV-2 Omicron variant (B.1.1.529), first discovered in November 2021, marked a major turning point in the COVID-19 pandemic due to its high transmissibility and immune evasion capabilities. The Omicron variant rapidly surpassed earlier variants, such as the Delta variant, thanks to a large number of mutations (over 30) in its spike protein, which enhanced its ability to bind to the human ACE2 receptor and evade immunity from prior infection or vaccination. While the Omicron variant generally causes milder disease than the Delta variant, its rapid spread led to widespread infection worldwide, placing significant strain on healthcare systems. The variant further diverged into multiple sublineages, including BA.1, BA.2, BA.4, and BA.5, each exhibiting distinct evolutionary advantages.

BA.5.5, a sublineage of the Omicron BA.5 variant, dominated global infections by mid-2022. It shares many features with BA.5, including key spike protein mutations such as L452R, F486V, and R493Q, which enhance immune evasion and transmissibility. However, BA.5.5 also carries other unique mutations, such as the ORF1b:I1566V mutation in the nonstructural protein, which may affect viral replication efficiency. Epidemiologically, BA.5.5 is particularly prevalent in regions such as South Asia and the Middle East, leading to localized surges in cases. Studies have shown that BA.5.5 retains the low-severity characteristics of Omicron but has a slight growth advantage over BA.5, likely due to subtle antigenic changes.