Abstract
BACKGROUND: The continual course of the pandemic points to the importance of studies on the rate and durability of protective immunity after infection or vaccination. AIMS: In this study, we aimed to monitor anti-nucleocapsid (N) and anti-spike (S) antibodies against SARS-CoV-2 nearly 9 months duration after infection. METHODS: Anti-nucleocapsid (N) (at 11-15-20-29-38 weeks) and anti-spike antibodies (at 11 and 38 weeks) against SARS-CoV-2 were monitored during 38 weeks after the initial symptoms of COVID-19. RESULTS: Of 37 cases between 18 and 57 years old, 54% were women. The findings showed that anti-N antibodies decreased significantly after the 15th week (between 15 and 20 weeks, p = 0.016; 20-29 weeks, p = 0.0009; and 29-38 weeks, p = 0.049). At the 38th week, mean antibody levels decreased 35% compared to the 11th week, and 8% of the cases turned negative results. Anti-N antibody average level was 56.48 on the 11th week (the cut-off index threshold ≥ 1). It was estimated statistically that it would decrease to an average of 20.48 in weeks 53-62. In females, average antibody levels of all measurements were lower than males (p > 0.05). Anti-S antibody levels 14% increased at 38th week compared to 11th week (quantitative positivity threshold ≥ 0.8 U/ml), and no cases were negative at 38th week. CONCLUSIONS: Patients had ≥ 90% positivity after at least 9 months of symptoms, both anti-N and anti-S antibodies. In all samples, both anti-N and anti-S antibody levels were lower in females. The findings suggest that the quantitative values of anti-S antibodies remained high for at least 9 months and could provide protection.