An Affordable Anti-SARS-COV-2 Spike Protein Elisa Test for Early Detection of IgG Seroconversion Suited for Large-Scale Surveillance Studies in Low-Income Countries

Abstract

Background: Accurate serological tests are essential tools to allow adequate monitoring and control of COVID-19 spread. Production of a low-cost and high-quality recombinant viral antigen can enable the development of reliable and affordable serological assays, which are urgently needed to facilitate epidemiological surveillance studies in low-income economies.Methods: Trimeric SARS-COV-2 spike (S) protein was produced in serum-free, suspension-adapted HEK293 cells. Highly purified S protein was used to develop an ELISA, named S-UFRJ test. It was standardized to work with different types of samples: (i) plasma or serum from venous blood samples; (ii) dried blood spots (DBS) from blood drops collected by finger prick.Findings: We developed a cost-effective, scalable technology to produce S protein based on its stable expression in HEK293 cells. The S-UFRJ ELISA displayed 98.4% specificity and sensitivity above 90% already 10 days after symptoms onset, allowing early detection of anti-S IgG seroconversion. Endpoint titers were shown to correlate with virus neutralization assessed as PRNT90. There was excellent agreement between plasma and DBS samples, significantly simplifying sample collection, storing and shipping. The overall cost per test was estimated to be approximately one US dollar.Interpretation: The S-UFRJ assay developed herein meets the quality requirements of high sensitivity and specificity. The low cost and the use of mailable DBS samples allow for serological surveillance of populations regardless of geographical and socio-economic aspects, with special relevance for public health policy actions in low-income countries.Funding Statement: This work was supported by Senai CETIQT, Senai DN and CTG, and by the Brazilian research funding agencies Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Instituto Serrapilheira.Declaration of Interests: The authors declare no competing interests.Ethics Approval Statement: Samples collected at the State Hematology Institute Hemorio followed a protocol approved by the local ethics committee (CEP Hemorio; approval #4008095). Samples collected at UFRJ COVID Screening Center followed a protocol approved by the national ethics committee (CONEP, Brazil; protocol #30161620000005257; approval #3953368).