Inactivated SARS-CoV-2 Variant Omicron, Lineage BF.5 (USA/MD-HP34985/2022)

The Omicron variant, first discovered in November 2021, marked a major turning point in the COVID-19 pandemic due to its unprecedented genetic divergence from earlier SARS-CoV-2 strains. The Omicron variant harbors numerous mutations, particularly in the spike protein, demonstrating enhanced transmissibility and immune evasion, rapidly becoming the dominant variant globally. Sublineages within the Omicron variant continue to evolve under the selective pressure of prior immunity and vaccination. Although the Omicron variant generally causes milder symptoms than the Delta variant, its high transmissibility has led to a surge in cases and placed significant strain on healthcare systems. The variant''s rapid evolution has spawned numerous sublineages, including BF.5, further enhancing its adaptive advantages.

BF.5, a descendant of the Omicron BA.5 sublineage, emerged in mid-2022 as part of the ongoing diversification of the Omicron variant. It inherits the characteristic mutations of BA.5, such as spike protein mutations (e.g., L452R, F486V, and R493Q), which enhance receptor binding and antibody escape. Other mutations in BF.5, including ORF7a:H47Y and nucleocapsid substitutions, may further affect viral adaptability or immune escape. From an epidemiological perspective, BF.5 is particularly prominent in regions such as China and the United States, triggering waves of infection due to its ability to circumvent natural immunity and vaccine-induced immunity. Studies have shown that BF.5 retains the high transmissibility of BA.5 but does not exhibit higher severity.