[Comparison of Two Different Quantitative Tests for Anti-Spike Measurement After Two Doses of Inactivated SARS-CoV-2 Vaccine in Healthcare Professionals].

Abstract

Serological tests developed to detect antibodies against severe acute respiratory syndrome Coronavirus disease-2 (SARS-CoV-2) antigens are used to demonstrate immunity level, vaccine efficacy and duration of protection. However, the evaluation of these tests and the interpretation of the results are still under investigation. In this study, it was aimed to compare the anti-spike measurement values in healthcare workers who have not experienced Coronavirus-2019 (COVID-19) after vaccination with two doses of inactivated SARS-CoV-2 vaccine with two commercial quantitative antibody detection tests which were used to give results in the same unit and work with different methods. The results obtained with Elecys Anti-SARS-CoV-2 S (Roche Diagnostics, Mannheim, Germany) and Aeskulisa Anti-SARS-CoV-2 S1 (Aesku diagnostics, Wendelsheim, Germany) kits of the serum samples of 90 healthcare workers were evaluated qualitatively and quantitatively in line with the recommendations of both manufacturers. Quantitative values given as units/mL (U/mL) were also evaluated by converting the binding antibody unit (BAU)/mL with the conversion factor obtained as a result of the studies carried out by the manufacturers with the World Health Organization anti-SARS-CoV-2 international standard. Positive results were obtained in 86 (95.6%) samples and negative results in 4 (4.4%) samples with the Elecsys kit; 55 (61.1%) positive, 20 (22.2%) negative and 15 (16.7%) intermediate results were obtained with the Aeskulisa kit. In common with both kits, negative results were obtained in four samples, and positive results were obtained in 55 samples. While the percent agreement observed with both kits was found to be 78.6 in 75 samples, excluding 15 samples in the intermediate with Aeskulisa kit, Cohen's kappa value was calculated as 0.26, indicating a close to moderate agreement, statistically. A high correlation was observed in the correlation analysis of the measurements of both kits (r= 0.611). When the scattering of the differences against the mean of the quantitative measurements made with both kits was examined by Bland-Altman analysis; higher measurements were determined with the Elecsys kit than with the Aeskulisa kit and the mean difference was found to be 58.68 ± 52.62. As a result of the studies carried out by the manufacturers, it was observed that the average difference decreased to 41.09 ± 50.22 when the U/mL values were converted to BAU/mL with the conversion factor. In the whole sampling, the measurements determined with the Elecsys kit were found to be 4.58 ± 3.44 times higher on average compared to the Aeskulisa kit while the measurements were found to be 2.35 ± 1.77 when the BAU/mL values were recalculated. The measurement values found with the Elecsys kit used in our study were found to be higher than that of Aeskulisa kit and qualitatively more positive results were obtained with Elecsys kit than with the Aeskulisa kit. In this study, Elecsys kit measurements were on average 4.06 times higher than Aeskulisa kit in samples (n= 55) with results compatible with both kits. The increase in these rates to 4.30 and 7.72 values, respectively, for 15 samples reported as intermediate and 16 as negative with the Aeskulisa kit, suggested that the success of quantitation decreased with the Aeskulisa kit at low antibody values. Since the harmonization of anti-SARS-CoV-2 tests has not yet been achieved, individual immune monitoring should be performed using the same method and even the results converted to BAU/mL should be specific to the antigen subunit.