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

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.