An updated RBD-Fc fusion vaccine booster increases neutralization of SARS-CoV-2 Omicron variants

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is a novel subset of coronavirus. To this day, the number of confirmed cases is over 500 million with more than 6 million deaths globally. SARS-CoV-2 keeps on evolving into different variants, including Alpha, Beta, Gamma, Delta, and Omicron. From November of 2021, the epidemic strain was Omicron, including B.1.1.529.1 (Omicron BA.1), B.1.1.529.2 (Omicron BA.2), B.1.1.529.2.12.1 (Omicron BA.2.12.1), B.1.1.529.3 (Omicron BA.3), B.1.1.529.4 (Omicron BA.4) and B.1.1.529.5 (Omicron BA.5). Omicron has spread all over the world and become the predominantly strain in most countries, especially Omicron BA.4 and Omicron BA.5. Nevertheless, the Delta variants (B.1.617.2, Delta 617) and some special variants also exist in in the crowd at the same period, such as B.1.640.2 (IHU) which was found in England. Omicron BA.1, Omicron BA.2, Omicron BA.3, Omicron BA.4, and Omicron BA.5 carry more than 30 mutations in the spike (S) protein as well as the receptor binding domain (RBD). These sublineages of Omicron variants share 11 mutations in the RBD region of virus, wherein Omicron BA.1 has 3 unique mutations, Omicron BA.2 has 4 unique mutations, Omicron BA.4 or Omicron BA.5 has 2 unique mutations. The RBD region of Omicron BA.5 is the same as the BA.4. 1 Given these differences, their antigenic properties cannot be assumed to be the same. Many of these mutations, e.g., K417Y, E484A, N501Y, have been predicted to affect neutralization epitopes. 2