Post-COVID-19 syndrome and humoral response association after one year in vaccinated and unvaccinated patients.

OBJECTIVES: To describe the impact of vaccination and the role of humoral responses on post-coronavirus disease 2019 (COVID-19) syndrome one year after the onset of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). METHODS: A prospective study. Interviews investigated post-COVID-19 syndrome 6 and 12 months after the disease onset of all adult in- and outpatients with COVID-19 attending Udine Hospital (March-May 2020). Vaccination status and two different serological assays to distinguish between response to vaccination (receptor-binding domain -RBD SARS-CoV-2 IgG) and/or natural infection (non-RBD- SARS-CoV-2 IgG) were also assessed. RESULTS: 479 individuals (52.6% female, mean age 53 years) were interviewed 13.5 months (0.6 SD) after acute infection. Post-COVID-19 syndrome was observed in 47.2% (226/479) of patients after one year. There were no significant differences in the worsening of post-COVID 19 symptoms (22.7% vs 15.8%, p = 0.209) among vaccinated (n=132) and unvaccinated (n=347) patients. The presence of non-RBD SARS-CoV-2 IgG induced by natural infection showed a significant association with post-COVID-19 syndrome (OR 1.35, 95% CI 1.11-1.64, p = 0.003), and median non-RBD SARS-CoV-2 IgG titres were significantly higher in long-haulers than in patients without symptoms 22 (IQR 9.7-37.2) vs 14.1 (IQR 5.4-31.3) kAU/L, p = 0.009) after one year. In contrast, the presence of RBD SARS-CoV-2 IgG was not associated with the occurrence of post-COVID-19 syndrome (>2500 U/mL vs 0.9-2500 U/mL, OR 1.36, 95% CI 0.62-3.00, p = 0.441) and RBD SARS-CoV-2 IgG titres were similar in long-haulers than in patients without symptoms (50% values > 2500 U/mL vs 55.6% values > 2500 U/mL, p = 0.451) CONCLUSIONS: The SARS-CoV-2 vaccination is not associated with the emergence of post-COVID-19 symptoms over one year after acute infection. The persistence of high serological titres response induced by natural infection but not by vaccination, may play a role in long-COVID-19.