Abstract
SARS-CoV-2 Omicron sub-variants are still emerging and become highly diversified, resulting in increased transmissibility and immune evasion ability. Neutralizing antibody is very important to fight against the variants. However, the ability of neutralizing antibody induced by early SARS-CoV-2 (D614G) primary infection has not been analyzed in detail against lately emerged Omicron variants, such as BA.5 and EG.5.1. In this study the sera from severe/critically infected patients of D614G were investigated the potency of neutralization activity against SARS-CoV-2 BA.5 and EG.5.1 by using live virus neutralization assay. The neutralizing activity was observed and analyzed in detail from day 1 until 7 post infection. The sera of both severe and critical patients showed cross neutralizing activity for BA.5, and even for EG.5.1. It is suggested that neutralizing antibodies targeting conserved epitopes are partly induced upon the primary infection as the result of robust immune response.