Comparative ELISA Detection of SARS-COV-2 Monoclonal Antibodies in Patients` Serum, Saliva, and Nasal Fluid in Iraq

Precise management of COVID-19 infection and global pandemic requires a precise assay of SARS-COV-2 antibodies. Spike protein and RBD specific serum monoclonal antibodies has been known to be elicited with the currently approved mRNA vaccine for COVID-19. Since combating SARS-CoV-2 infection begins as early at the viral entry port, mediated by mucosal immunity; whether the currently approved vaccines have the capacity to elicit mucosal immunity is still to be studied. Method; We conducted our research to detect SARS-Cov-2 IgA-RBD and IgG-NCP, in a set of a randomized three patients’ groups (total 55 subjects, randomized into 20 (Non previously infected control, 20 fully vaccinated people from AlSalam teaching hospital vaccination ward upon receiving the vaccine doses, and 15 patients newly recovered from SARS-CoV-2 infection from AlShifaa quarantine hospital after remission from COVID-19 infection and preparing to discharge) in three fluid samples serum, saliva and nasal fluid, for a total of three samples per participant, to make a total of 165 samples to be tested, using a commercial immunoassay kit (Anti-SARS-CoV-2 ELISA RBD IgA, and Anti-SARS- CoV-2 NCP ELISA IgG) the study was designed to assess the immunoglobulins levels in each sample from different health status and anatomical locations to give the statistical difference and the correct conclusion regarding this study. Statistical analysis was performed using SPSS version 24, as well as Microsoft excel version (16.0.15028), test equations were performed via Mann-Whitney U Test, as well as The Kruskal-Wallis H test, to evaluate the non-gaussian distribution among the study group, for each of the outcomes, p < 0.05 was undertaken as statistically significant. Results; Our work showed that two doses of mRNA BNT162b2 vaccine Comirnaty (Pfizer/BioNTech, New York, NY, USA), elicited a robust anti SARS-CoV-2 nasal and salivary IgA and IgG monoclonal antibody protection (as compared to control 0.625 COI, the vaccinated subjects resulted in a higher median salivary concentration of IgG NCP values as 1.69 COI, with a p-value of 0.0001. same goes for median salivary concentration of IgA RBD with value of 2.875 ± 1.276, as compared to control median values of 0.667 ± 0.208), (as compared to control 0.462 ± 0.2369, the vaccinated subjects resulted in a higher median nasal concentration of IgG NCP values as 1.944 ± 0.694, with a p-value of 0.0001. Same goes for median nasal concentration of IgA RBD with value of 1.941 ± 0.53, as compared to control median values of 0.681 ± 0.226). Two injections 25 days a part shown to trigger a stronger titer of protective immunity as compared to single early shot, still it`s less robust compared to the titers measured for the recovered subjects from COVID-19 infection. Taking into consideration that there was a lack of trustable ELISA based assays with specially designed kit for this purpose, focusing on nasal and salivary secretions, the current study that our pre investigational and investigational data are consistent. The results of this study indicates that a protective antigen specific nasal and salivary monoclonal antibody, can be triggered following proper vaccination regimen with mRNA COVID-19 vaccine, so this paves the way for using mucosal protective antibodies detection kits, as a suitable alternative option as a less invasive method compared to serum investigations, for detecting the protection against SARS-Cov-2 infection, induced by vaccine. The vaccinated subjects are significantly better tested via IgA in Saliva as compared to IgG, because of the higher median values for the IgA vs IgG, 2.875 ± 1.276 and 2.083 ± 1.610 respectively with a p-value of 0.008. in a similar state the IgA is the best test for the convalescent subjects in term of nasal fluid samples investigations, as the median value are comparatively higher than median value of IgG, 2.024 ± 0.520 and 1.786 ± 1.115 respectively.