Evaluation of Anti-SARS-CoV-2 IgG before and after vaccination in subjects with and without previous COVID-19 disease

ABSTRACT

BACKGROUND-AIM Although more than two years have passed since the beginning of the SARS-CoV-2 pandemic, the interest of Public Health in the development and administration of effective anti-COVID-19 vaccines continues.We aimed to test the antibody response to SARS-CoV-2 vaccination in patients with and without previous infection. METHODS From June 2021 to November 2021, we recruited 203 patients who were going to receive vaccination against SARS-CoV-2 123 women (60.6%) with a median age of 44 years (IQR 33-56) and 80 men (39.4%) with a median age of 43 years (IQR 32-53);78 patients reported previous SARS-CoV-2 infection (41 women, 37 men). 74 out of 203 were healthy subjects, 84 reported mild to medium allergic history and 45 other diseases. 97.4% of subjects received BioNTech/Pfizer vaccination and, according to Ministerial Dispositions, patients with previous SARS-CoV-2 infection received a single dose (group 1), other patients received two (group 2). After 3 months, 98 subjects received a third dose (57 BioNTech/Pfizer and 41 half a dose of Spikevax-Moderna).The antibody response to vaccination was measured on blood samples collected before vaccination (T0), 10 days after the first dose of vaccination (T10), 15 (T15), 90 (T90) and 180 (T180) days after the second or only vaccination. Samples were tested using Access SARS-CoV-2 IgG (1st IS) on Access UniCelDxI 800 (Beckman Coulter s.r.l.). RESULTS The comparison between median concentrations in our groups showed a statistically significant difference (p<0.001) at T0, T15 and T90, but not at T180 (p=0.713). At T0 and T90 the SARS-CoV-2 IgG concentration was higher in group 1, while at T15 it was higher in group 2. At T90 the antibody titer dropped in all patients, but the decrease was higher in group 1. 77 SARS-CoV-2 infections occurred after vaccination (4.2% between T15 and T90, 95.7% between T90 and T180). CONCLUSIONS We confirm that the antibody titer is significantly associated with a having had previous SARSCoV-2 infection, but not with age and sex. The probability of contracting the infection after vaccination increases after three months from primary vaccination, confirming the efficacy of vaccination as a preventive measure against SARS-CoV-2 infections and the need of booster administrations.