Epidemiological and immunological characteristics of middle-aged and elderly people in housing estates after Omicron BA.5 wave in Jinan, China.

A great number of COVID-19 patients was caused by Omicron BA.5 subvariant between December 2022 and January 2023 after the end of the zero-COVID-19 policy in China. In this study, we clarified the epidemiological and immunological characteristics of 457 enrolled middle-aged and elderly population in two housing estates after Omicron BA.5 wave. A total of 89.9 % (411/457) individuals have suffered Omicron BA.5 infection, among which 78.1 % (321/411) were symptomatic. The elderly patients were more likely to show fatigue and had longer symptomatic period than that of middle-aged patients post Omicron BA.5 infection. Omicron XBB and BA.2.86 subvariants extensively escaped the immunity elicited by Omicron BA.5 infection. The level of neutralizing antibody was mostly affected by vaccination doses rather than underlying disease status in these participants. It is very important to strengthen the epidemiological investigation and immune resistance assessment among elderly population for control of emerging SARS-CoV-2 variants.