This study aimed to evaluate the presence of anti-SARS-CoV-2 antibodies in the general population and in COVID-19 convalescents six months post-infection. The study included two groups: Group I comprised 232 individuals recovering from COVID-19, and Group II included 544 participants from a population-based cohort. Anti-nucleocapsid (anti-N) antibodies were measured using the Elecsys Anti-SARS-CoV-2 assay, while anti-spike (anti-S) antibodies were assessed using the LIAISON SARS-CoV-2 S1/S2 IgG test. Following the Omicron wave, the general population showed a gradual increase in antibody prevalence, reaching 92.5% for anti-S and 69.7% for anti-N antibodies. Among COVID-19 convalescents, 6 months post-infection, 4.3% and 3.7% failed to develop detectable anti-S and anti-N antibodies, respectively. Among vaccinated individuals, 1% did not produce anti-S antibodies. Non-responders were generally older than responders, while sex had no significant effect. Comparisons of antibody levels six months post-infection revealed higher anti-N titers in previously infected patients compared to the general population. Notably, 17.4% of the general population without prior COVID-19 or vaccination had anti-N antibodies, and 9% had anti-S antibodies. The high prevalence of anti-N antibodies among individuals without reported COVID-19 history, even after the official end of the pandemic, indicates widespread SARS-CoV-2 exposure and frequent asymptomatic or undiagnosed infections. These findings have important implications for public health surveillance.