Analysis of Covid-19 Neutralizing Antibody Levels Post Vaccination using Ichroma™ and iFlash Covid-19 Nab

Background: One of the efforts to control SARS-CoV-2 infection in health workers is vaccination. In this study, the levels of SARS-CoV-2 neutralizing antibody (nAb) in health workers were measured with Ichroma and iFlash. Methods: This study applied an observational analytic design with a prospective cohort and was conducted at Dr. Soetomo Regional Public Hospital, Surabaya, from January to November 2021. The population of this study included a total of 75 health workers after taking the second dose of the SARS-CoV-2 (Sinovac) vaccine. The Covid-19 NAb levels of the population were tested with Ichroma and iFlash on day 0 before vaccination, as well as days 14 and 28, and months 3 and 6 after vaccination. Results: The Friedman test indicated a significant difference in NAb levels according to the iFlash test on day 14, day 28, month 3, and month 6 compared to those before vaccination (p < 0.05). The Wilcoxon test revealed a significant difference in NAb levels on day 14, day 28, month 3, and month 6. The results of the Cochran test showed a significant difference in the positivity of NAb according to the Ichroma test on day 14, day 28, month 3, and month 6 compared to those before vaccination (p < 0.05). McNemar's test demonstrated that the COI at month 3 was not significantly different from that before vaccination; The COI at month 6 was not significantly different from those at days 14 and 28. The results of the Pearson correlation test and Bland–Altman plot indicated a moderate correlation between Ichroma and iFlash (r = 0.592, p = 0.002). Conclusion: Neutralizing antibodies for Covid-19 were formed after day 14 and started to increase on day 28 and started to decrease in months 3 and 6. The levels of NAb for Covid-19 were measured with Ichroma and iFlash in roughly the same pattern and had a moderate positive correlation.