Inactivated SARS-CoV-2 Variant Omicron, Lineage BQ.1.3 (USA/NY-Wadsworth-22047869-01/2022)

The Omicron subvariant, BQ.1.3, is a descendant of the BA.5 lineage and is more contagious due to its ability to evade innate and adaptive immune responses. This variant primarily spreads through respiratory droplets and aerosols and has enhanced binding affinity for the human angiotensin-converting enzyme 2 (ACE2) receptor, facilitating rapid viral entry into cells. Mutations in the spike protein of BQ.1.3 (particularly R346T and K444T) impair the neutralizing effect of vaccine-induced antibodies and immunity generated by prior infection, increasing the risk of reinfection. While its pathogenesis is less severe than earlier variants such as Delta, it still has the ability to cause upper respiratory tract infections, with symptoms ranging from mild (e.g., fever, cough) to moderate (e.g., pneumonia in susceptible individuals).

The BQ.1.3 genome comprises approximately 30,000 nucleotides, encoding structural proteins (spike, envelope, membrane, and nucleocapsid) and nonstructural proteins (e.g., RNA-dependent RNA polymerase). Its most notable feature is a severe mutation in the spike protein, with over 30 amino acid changes compared to the Wuhan-Hu-1 strain. Key mutations, including N460K, F486V, and D1199N, alter the spike protein''s conformation, reducing antibody binding while maintaining ACE2 affinity. This variant also possesses deletions (such as Δ69–70) that may enhance viral replication efficiency. In addition to the spike protein, mutations in the nucleocapsid protein (such as P13L) and membrane protein may also contribute to viral assembly and immune evasion.