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

www.nature.com/scientificreports OPEN Development of an in‑house quantitative ELISA for the evaluation of different Covid‑19 vaccines in humans Mariem Gdoura1,2,3, Fatma Ben Ghaloum4, Meriem Ben Hamida1, Wafa Chamsa1, Henda Triki1,2 & Chokri Bahloul4* 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 SARSCoV-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. The ongoing global pandemic of coronavirus disease 2019 (COVID-19) is caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), identified for the first time in December 2019 in Wuhan, China. The disease was declared by the World Health Organization (WHO) as a pandemic on the 11th of March 20201. Up to 23 December 2021, more than 276 million cumulative cases and 5.3 million cumulative deaths have been reported2. The high burden of the disease triggered a race towards the development and distribution of effective vaccines, to slow the viral transmission, lower the disease severity and reduce the mortality. While typical vaccine development can take up to 10–15 years, COVID-19 vaccines needed less than a year after the identification of COVID-193. To overcome such a challenge, clinical development, manufacturing scale-up and distribution occurred in parallel for all the COVID-19 vaccines. As of 21 December 2021, 137 vaccines are under clinical trials, with 10 in Phase 4 after being approved for emergency use in humans4. Different platforms of approved vaccines are currently being administered all over the world, mRNA vaccines (Pfizer-BioNTech, Moderna); recombinant adenovirus vectored vaccines (AstraZeneca, Cansino, Gamaleya, Johnson Pharm) and inactivated vaccines (Sinopharm, Sinovac). Phase 4 clinical trials, also called post-marketing surveillance trials, studies the side effects caused over time that were not seen in earlier trials by a new vaccine, are currently being performed. These trials also study how well the vaccine works over a long period of time. Although the introduction of Covid-19 vaccines contributed to decrease the burden of the disease in many parts of the world, new cases have increased significantly in many countries in both vaccinated and 1 Laboratory of Clinical Virology, Institut Pasteur de Tunis, Tunis, Tunisia. 2Research Laboratory « Virus, Vector and Hosts » LR20IPT02, Tunis, Tunisia. 3Faculty of Pharmacy of Monastir, University of Monastir, Monastir, Tunisia. 4Vaccinologie et Développement Biotechnologique, LR11IPT01 Microbiologie Moléculaire, Institut Pasteur de Tunis, Université de Tunis El Manar, 13, Place Pasteur, BP 74, 1002 Tunis‑Belvedere, Tunisia. *email: Scientific Reports | (2022) 12:11298 | https://doi.org/10.1038/s41598-022-15378-1 1 Vol.:(0123456789) www.nature.com/scientificreports/ Vaccination against COVID-19 Day 14-40* Day 10-100 Post-second shot No COVID-19 Histories COVID-19+ by RT-PCR First vaccination shot Single vaccination shot Second vaccination shot Sampling Day 10-100 Post-vaccination Sampling Figure 1.  Flowchart for vaccination and sampling procedures. * Second shot, when applicable, was administered according to the manufacturer recommendations as mentioned in “Material and methods”. non-vaccinated populations due to the emergence of new v ariants5. Recent data suggest that mRNA vaccines including Pfizer/BioNTech and Moderna have higher efficacy and protection against COVID-19 i nfection5. Vaccines against COVID-19 are not reaching many people in developing countries. Less than 1% of people in low-income countries are fully vaccinated, and just 10% in lower-middle-income countries, are fully vaccinated compared with more than half in high-income c ountries6. In Tunisia, from 3 January 2020 to 23 December 2021, there have been 721,797 confirmed cases of COVID-19 and 25,491 deaths, reported to the WHO. As of 23 December 2021, more than 12.6 million vaccine doses have been administered7. Up to 20 December 2021, 46.7% of the Tunisian population were fully vaccinated8. In Tunisia, all the platforms of COVID-19 vaccines have been used (Pfizer/BioNtech, Moderna, Spoutnik, AstraZeneca, Johnson & Johnson, Sinovac and Sinopharm). Recent studies indicate that binding and neutralizing SARS-CoV-2 antibodies elicited by natural infection or vaccination persist for more than 6 months although their concentration decreases over time9. The passive transfer of neutralizing antibodies and protection are correlated in non-human p rimates10. While such a link has not yet been defined in humans, individuals with high neutralizing antibody titers could well be better protected against SARS-CoV-2. It was reported that neutralizing antibodies are highly correlated with protection due to their ability to block the viruses from entering the host c ells11. A recent investigation in France reported that ELISA concentrations between 13 and 141 BAU (Binding Antibody Units)/ml provided only 12.4% protection against SARS-CoV-2; concentrations between 141 and 1700 BAU/ml provided 89.3% protection; and concentrations of 1700 BAU/ml and over provided full protection12. Therefore, reliable and highly efficient serology assays are urgently needed to evaluate the efficiency of the administered COVID-19 vaccines. In our investigation, we have set up and validated a quantitative ELISA technique using a Baculovirus recombinant full length SARS-CoV-2 Spike Glycoprotein. This ELISA technique allowed us to assess and compare the efficiency of the (...truncated)