Detection of SARS-CoV-2 Antibodies in Oral Fluid Using a Magnetic Particle-Based Chemiluminescence Immunoassay - Beijing Municipality, China, 2021.

Introduction: Oral fluids (OFs) have been broadly used as non-invasive samples for evaluating protective IgG antibodies from natural infection or vaccination, especially in pediatric populations. Methods: Paired OF and serum were collected from both individuals who received a booster dose of the inactive coronavirus disease 2019 (COVID-19) vaccine as well as those who did not have a history of COVID-19 vaccination and infection (as the control group). The total human IgG antibody (HIgG) content was evaluated as a marker of OF sampling quality. An in-house adapted magnetic particle-based chemiluminescence immunoassay was used for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) IgG antibody detection in the OF. The SARS-CoV-2 IgG antibody in the serum samples was detected using a commercial immunoassay. Results: In total, 579 paired OF and serum samples were collected. An additional 172 OF samples were collected from preschool children. The results indicated that the HIgG concentration in qualified OF samples should be higher than 0.3 µg/mL. Compared to the serum assay, the in-house OF immunoassay for detecting IgG antibodies against SARS-CoV-2 had 95.06% accuracy, 95.03% sensitivity, and 100% specificity. Conclusions: Overall, the in-house immunoassay for detecting SARS-CoV-2 IgG antibodies in OF showed high potential for application towards serological surveillance and immunization effect assessment after large-scale, inactive COVID-19 vaccination in China.