Neutralizing antibody test supports booster strategy for young individuals after SARS-CoV-2 Omicron breakthrough

The SARS-CoV-2 Omicron variant, since its initial detection, has rapidly spread across the globe, becoming the dominant strain. It is important to study the immune response of SARS-CoV-2 Omicron variant due to its remarkable ability to escape the majority of existing SARS-CoV-2 neutralizing antibodies. The surge in SARS-CoV-2 Omicron infections among most Chinese residents by the end of 2022 provides a unique opportunity to understand immune system's response to Omicron in populations with limited exposure to prior SARS-CoV-2 variants. We tested the levels of IgG, IgA, and IgM specific to the prototype SARS-CoV-2 RBD (receptor-binding domain) in blood samples from 636 individuals by chemical luminescence assay, ELISA and pseudovirus-based neutralization assay. Inoculation with inactivated prototype SARS-CoV-2 vaccines or recombinant protein vaccines showed higher IgG levels after infection than the unvaccinated individuals. Moreover, the age resulted in different IgG levels after the Omicron infection as IgG level of the patients aged > 60 years was lower than that of patients aged