The Validation of a Hemagglutination Inhibition Assay That Detects Antibodies Against a Newcastle Disease Virus-Based Vaccine Vector in Human Serum Samples

Background: An NDV-based vector has been used as a veterinary vaccine and, recently, as a human COVID-19 vaccine. However, data for the potential immune response against the vector in humans are scarce; therefore, it is important to evaluate the levels of antibodies produced. The HI assay is the gold standard for assessing the humoral response against NDV in poultry serum. Objective: Here, the objective was to validate the HI assay against the NDV-vectored vaccine to analyze antibodies in human serum. Methods: First, we standardized the conditions in human sera before validation. Results: The results for analytical performance in terms of selectivity, sensitivity, specificity, and positive and negative predictive values, as well as positive and negative diagnostic reliability, indicate that the assay is highly selective, allowing clear discrimination between positive and negative samples. Regarding repeatability and intermediate precision, we demonstrated that the assay has the precision to obtain consistent results, guaranteeing their reliability and truthfulness. Finally, the results regarding accuracy, linearity, and robustness indicate that the assay is accurate across the evaluated concentration intervals, with a linear correlation between low and high levels, and demonstrate that it is robust and consistent when serum–antigen interaction times are changed. Conclusions: We conclude that the suitability of the analytical method for its intended use is confirmed, guaranteeing the reliability of the results obtained under the established operating conditions.