Longitudinal profile of neutralizing and binding antibodies in vaccinated and convalescent COVID‐19 cohorts by chemiluminescent immunoassays

INTRODUCTION: Surrogate rapid serological assay was urgently demanded for accessibly interpretation of immunity potency and duration of neutralizing antibody against SARS‐CoV‐2. The longitudinal trajectory of antibody profile with a reliable large‐scale assay was crucial to judge the protective immune status, avoid futile therapy and provide insight into the booster vaccination minimizing the risk of COVID‐19. METHODS: A total of 195 volunteers were enrolled for a two‐doses procedure (0 and 28 days) of inactive vaccination, as well as ten COVID‐19 convalescents. The serum was collected at six time point and detected by chemiluminescent immunoassay with SARS‐CoV‐2 neutralizing antibody (Nab), SARS‐CoV‐2 RBD immunoglobulin G (IgG) antibody (RBD IgG) and RBD total antibody. The diagnostic results and the correlation of antibody level were evaluated among three serological (Nab, RBD IgG, and RBD total antibody) assay, as well as with an authorized cPass kit (Nab). Referred to the assay‐specific threshold, the seroconversion rate and dynamic titer of antibody were exhibited from 0 to 56 days since vaccination. RESULTS: There was no difference observed with diagnostic results between neutralizing and RBD IgG antibody (p > 0.05). Both diagnostic results of neutralizing and RBD IgG antibody testing differentiated from RBD total antibody assay (p < 0.05). The coefficient of correlation (R) was above 0.90 among the levels of those three antibodies, more than 0.60 in comparison with neutralizing antibody by cPass enzyme‐linked immunoassay. The “S” varying pattern for various antibodies level was observed with time extension after vaccination. The seroconversion rate was below 11.1% in 2 weeks after the priming dose, while the value climbed to 81% in 1 week after the boosting dose. The seroconversion rate was maintained around 91%. The inactive vaccine elicited 81‐fold higher antibody levels after finished the vaccination schedule than that at the basic point. Besides, the level of neutralizing antibody induced by vaccine was found with a 0.2‐fold ratio by comparison with that in COVID‐19 convalescents. CONCLUSION: The humoral immune response products including SARS‐CoV‐2 neutralizing, RBD IgG antibody and total antibody and the varying pattern of the antibody profile could be rapidly detected by CILA method. Meanwhile, the continuing and dynamic determination was attributed to evaluate the protection effect of humoral immunity against the SARS‐CoV‐2 infection.