Development of an in-house quantitative ELISA for the evaluation of different Covid-19 vaccines in humans

Reliable serological assays are needed to understand the real impact of COVID-19. In order to compare the efficiency of different COVID-19 vaccines used in the National Vaccination Program in Tunisia, we have developed a quantitative in-house ELISA. The ELISA is based on the ectodomain of the SARS-CoV-2 Spike Baculovirus recombinant protein. We used a panel of 145 COVID-19 RT-PCR positive serum samples and 116 pre-pandemic serum samples as a negative panel. The validation was carried out by comparison to four commercial techniques (Vidas SARS-CoV-2 IgG anti-RBD Biomérieux, Elecsys Anti-Nucleocapsid of SARS-CoV-2 Roche, cPass GenScript and the quantitative Elecsys Anti-RBD of SARS-CoV-2, Roche). For the evaluation of the National Vaccination campaign, we have included 115 recipients who received one of the approved vaccines. The qualitative performances of the developed ELISA gave 96% sensitivity, 97.5% specificity and 0.968 accuracy. For the evaluation of the different brand of vaccines in recipients not previously infected with SARS-CoV-2, it seems that mRNA vaccine of Pfizer/BioNTech has shown a higher efficacy compared to inactivated virus vaccines. COVID-19 convalescent individuals have generated poor antibody responses. Nevertheless, when they are vaccinated with any brand of the COVID-19 vaccines, many of them mounted an exponential increase of the induced immune responses, qualified as a "hybrid vigor immunity". Our developed in-house ELISA seems to be very efficient in evaluating the effectiveness of anti-COVID-19 vaccination. Platforms based on mRNA vaccine are better performing than those based on inactivated virus.