Abstract
From December 2022 to January 2023, the SARS-CoV-2 Omicron BA.5/BF.7 variant significantly impacted mainland China. While most COVID-19 patients experienced mild symptoms and were treated as outpatients or at home, some cases progressed to severe illness, necessitating hospitalization or even resulting in death. To better understand this outbreak and forecast future waves as SARS-CoV-2 continues to evolve, it is crucial to assess the titer of neutralizing antibodies (Nab) for evaluating the establishment of an immune barrier. In this study, we investigated the dynamic evolution of humoral immunity following the breakthrough infection wave driven by the SARS-CoV-2 Omicron BA.5/BF.7 variant in southwest China. Over a period of more than one year, we analyzed 3128 serum samples collected monthly to delineate the kinetics of Nab responses in a large cohort. Our data revealed a pronounced surge in Nab titers immediately after the December 2022-January 2023 outbreak, particularly among individuals primed with two or three doses of vaccine. As the epidemic progressed, emerging variants such as XBB.1.5, EG.5, and JN.1 elicited distinct immunological responses and demonstrated varying capacities for immune escape. Our findings underscore the rapid antigenic evolution of SARS-CoV-2 and the consequent challenges in sustaining effective population-level immunity, thereby advocating for continual surveillance and adaptive vaccine immunogen updates.