The outbreak of SARS-CoV-2 Omicron lineages, immune escape, and vaccine effectivity.

As of November 2021, several SARS-CoV-2 variants appeared and became dominant epidemic strains in many countries, including five variants of concern (VOCs) Alpha, Beta, Gamma, Delta, and Omicron defined by the World Health Organization during the COVID-19 pandemic. As of August 2022, Omicron is classified into five main lineages, BA.1, BA.2, BA.3, BA.4, BA.5 and some sublineages (BA.1.1, BA.2.12.1, BA.2.11, BA.2.75, BA.4.6) (https://www.gisaid.org/). Compared to the previous VOCs (Alpha, Beta, Gamma, and Delta), all the Omicron lineages have the most highly mutations in the spike protein, and with 50 mutations accumulated throughout the genome. Early data indicated that Omicron BA.2 sublineage had higher infectivity and more immune escape than the early wild-type (WT) strain, the previous VOCs, and BA.1. Recently, global surveillance data suggest a higher transmissibility of BA.4/BA.5 than BA.1, BA.1.1 and BA.2, and BA.4/BA.5 is becoming dominant strain in many countries globally.