Agency FAPESP* – Researchers from the Institute of Biomedical Sciences of the University of São Paulo (ICB-USP) attested to the effectiveness of three new serological tests for COVID-19. Developed at the ICB itself, the tests use the ELISA method (enzyme-linked immunosorbent assay) for the detection of antibodies against the SARS-CoV-2 virus and had their effectiveness compared with another test already in use on the market, the Elecsys, from pharmaceutical Roche .
Published in the magazine Frontiers in Cellular and Infection Microbiology, the work was supported by FAPESP and was based on 1,119 blood samples from people who had or had not had contact with the disease. The testing was conducted at the University Hospital (HU) of USP throughout 2020 and, therefore, shows a scenario without vaccines.
In the evaluation, the Elecsys test, marketed by pharmaceutical Roche, guaranteed 96.92% sensitivity (ability to detect positive cases) and 98.78% specificity (ability to identify negative cases). The performance of the methods developed at the ICB was approximated. The N-ELISA test, which evaluates a complete coronavirus N protein, recorded 93.94% sensitivity and 94.40% specificity. The RBD-ELISA test, which uses a fragment of the protein spike of the coronavirus, obtained 90.91% and 88.80% efficiency in these two criteria, respectively, while the Delta-S1-ELISA, which uses another fragment of the spikeshowed a sensitivity of 77.27% and a specificity of 76%.
“We obtained such good results with the N-ELISA test that we can imagine it being used commercially in the future. By adopting a protein that is used commercially, unlike our other two tests, the path is potentially shorter”, highlights Robert Andreata- Santos, PhD in microbiology and first author of the study.
In addition, RBD-ELISA and N-ELISA tests may, in the future, be used to differentiate whether the antibody was induced by vaccination or infection. “Being effective in detecting antibodies against the RBD protein, which is present in all current vaccine formulations, as well as against the N protein, related to cases of exposure to the coronavirus, indicates that in future studies there will be the possibility of differentiating antibodies produced against vaccine or against infection when both tests are used”, says Andreata-Santos.
Gold standard of analysis
All exams were validated against the coronavirus itself through the neutralization test, considered the gold standard for this type of analysis. Blood serum was applied to the test to distinguish which samples neutralized and which samples did not neutralize SARS-CoV-2, and neutralized samples were considered positive for COVID-19. These results were then compared with the results of the ELISA tests.
The neutralization test, which requires a laboratory with a high level of biosafety as it involves viral manipulation, has high sensitivities and specificities, as it is able to calculate the patient’s neutralizing antibody load. “Furthermore, as SARS-CoV-2 has been neutralized, the possibility that antibodies created due to infection by the coronavirus or another pathogen will cross-react is extremely low”, adds Andreata-Santos.
The method is also able to identify whether an antibody is neutralizing (it can prevent further infections) or whether it is a binding-only antibody (it only recognizes a region of the virus). In this way, the methodology eliminates almost all doubts that may arise regarding the effectiveness data of the ELISA tests.
The study was carried out within the scope of the Thematic Project “Discovery of antigens and development of serological diagnostic methods and vaccine strategies against the Zika Virus (ZIKV)”, coordinated by Luis Carlos de Souza Ferreira. It had the collaboration of Paulo Margarido (HU-USP), Ricardo Fock (HU-USP) and Juliana Bannwart in the collection of serum and evaluation of the samples by Elecsys, in addition to groups of researchers coordinated by Edison Luiz Durigon, Silvia Beatriz Boscardin and Cristiane Rodrigues Guzzo – all from ICB-USP.
The project also had the support of the Coordination for the Improvement of Higher Education Personnel (Capes) and the National Council for Scientific and Technological Development (CNPq).
The article Validation of Serological Methods for COVID-19 and Retrospective Screening of Health Employees and Visitors to the São Paulo University Hospital, Brazil can be read at: https://pubmed.ncbi.nlm.nih.gov/35719329/.
* With information from the ICB-USP Communications Office.
This text was originally published by Agência FAPESP under the Creative Commons CC-BY-NC-ND license.