Diverse immune responses in vaccinated individuals with and without symptoms after omicron exposure during the recent outbreak in Guangzhou, China.

ABSTRACT

Objectives: During the recent wave of coronavirus disease 2019 (COVID-19) infections in China, most individuals have been vaccinated and exposed to the omicron variant. In the present study, two cohorts were observed in the vaccinated population vaccinated individuals with symptoms (VIWS) and those without symptoms (VIWOS). Our study aimed to characterize the antibody response in two cohorts VIWS and VIWOS. Methods: A questionnaire survey was conducted in the community. Blood and saliva samples were collected from 124 individuals in the VIWS and VIWOS cohorts. Capture enzyme-linked immunosorbent assay (ELISA) was performed to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) specific antibodies. Results: The questionnaire survey revealed that 30.0 % (302/1005) of individuals in the older adult group (≥65 years) experienced no symptoms, whereas the rate of individuals without symptoms in the younger group (<65 years) was 17.8 % (166/932). Nucleocapsid (N)-specific IgM (N-IgM) was detected in the blood samples at a rate of 69.2 % (54/78) in the VIWS cohort. The positivity rate for N-specific IgA (N-IgA) was 93.6 % (73/78). In addition, the positivity rates of spike (S)-specific IgA (S-IgA) and N-IgA detected in saliva samples were 42 % (21/50) and 54 % (27/50), respectively. Both N-IgA positivity and negativity were observed in the VIWOS cohort. The detection rate of N-IgM positivity was 57.1 % (12/21) in the N-IgA-positive group. In addition, 54.3 % (25/46) of the vaccinated individuals without symptoms were IgA-negative. Conclusions: Our study indicates that substantial N-specific antibodies were induced during omicron infection and that testing for N-IgA in both blood and saliva may aid in the diagnosis of SARS-CoV-2 infection in vaccinated populations.