How many is good enough? An analysis of serological follow-up after vaccination against SARS-CoV-2

Introduction. Despite vaccinations available worldwide, patients and healthcare workers still struggle with COVID-19. Previously we observed in some convalescents surprisingly lower antibody levels after a second dose of SARS-CoV-2 vaccine compared to the first dose. Six months after full vaccination we obtained follow-up results of 87 patients divided into 3 groups: (A) convalescents with higher antibody levels after second dose of vaccine compared to first dose, (B) naive patients, (C) convalescents with decreasing antibody level after second dose compared to first dose.Materials and Methods. Patients' anti-SARS-CoV-2 antibody levels were checked by the anti-SARS-CoV-2 QuantiVac ELISA (IgG) (EUROIMMUN MedicinischeLabordiagnostica AG, Luebeck, Germany) test, as before, and prior to the blood sampling patients completed a questionnaire regarding, inter alia, general condition, smoking, flu vaccination.Results Thanks to this follow-up we concluded that none of the patients suffered from symptomatic SARS-CoV-2 infection within 6 months after vaccination. Decline of antibody levels 6 months after vaccination was observed in all groups. Convalescent group A lost more antibodies in the mentioned period of time than group B or C. Group C presented still high results, higher than in group B (p = 0.007), but lower than in group A (p = 0.048).Conclusions. Temporary decrease of antibody levels in convalescents after the second dose of SARS-CoV-2 vaccination did not imply further consequences in the form of important antibody level differences 6 months after vaccination. Patients' overweight could have an impact on antibody production but only after natural infection. It did not affect obtained results after vaccinations.