SARS-CoV-2 neutralizing antibody determination after vaccination using spectrophotometric measurement of lateral flow immunochromatography.

Neutralizing antibody titers have been found to be strongly correlated with observed vaccine effectiveness against symptomatic and severe COVID-19. Few non-high complexity assays are currently available to detect the presence of neutralizing antibodies. This retrospective single-center cross-sectional study compared the performance of a lateral flow immunochromatography assay coupled with a spectrophotometric measurement system for detecting SARS-CoV-2 neutralizing antibodies against an enzyme-linked immunosorbent assay (ELISA) neutralization antibody assay in the context of post-vaccination responses. The limit of detection was similar to the ELISA with strong linearity throughout the measuring interval. Repeatability, interfering substances, and cross-reactivity studies were found to be robust. Results for 274 plasma samples on whom SARS-CoV-2 RNA test and vaccination status, including vaccination number and manufacturer, was known showed a positive predictive value (PPV) of 99.0% (CI 96.4-99.7%) and a negative predictive value (NPV) of 91.9% (CI 83.4-96.2%) compared to ELISA. The PPV for all vaccination number and manufacturer subgroups was > 95% except for those individuals who had only 1 Pfizer vaccination (PPV of 80%). The NPV for those who were PCR positive with no vaccinations was 100% while only 88.1% for those without a previous positive test or vaccination. The NPV for those with Pfizer vaccinations was 80% in contrast to 100% for those with Moderna vaccinations. Alternative methodologies requiring less sophisticated laboratory support to measure neutralizing antibodies may be useful to measure vaccine responses.