Table 1.

Humoral immunogenicity before and after fourth dose of COVID-19 heterologous vaccination in poor/non-responders ARD patients

Groups	After third dose	After fourth dose	P-value
Anti-S1/S2 IgG positivity, n (%)	109 (66.4)	156 (95.1)	<0.001
Anti-S1/S2 IgG GMT (95% CI), AU/mL	29.5 (23.3, 37.4)	215.8 (180.5, 257.9)	<0.001
NAb positivity, n (%)	9 (5.5)	137 (83.5)	<0.001
Neutralizing activity, median (IQR), %	49.2 (38.1–83.3)	90.6 (66.2–96.2)	0.101

Frequencies of subjects with positive anti-SARS-CoV-2 S1/S2 IgG and NAb are expressed as number (%). Positivity for anti-SARS-CoV-2 S1/S2 IgG was defined as post-vaccination titre ≥15 AU/mL by Indirect ELISA (LIAISON^® SARS-CoV-2 S1/S2 IgG, DiaSorin, Italy). Positivity for NAb was defined as a neutralizing activity ≥30% (cPass sVNT Kit, GenScript, Piscataway, NJ, USA). Anti-S1/S2 IgG antibody titres are expressed as GMT with 95% CI and percentage of neutralizing activity of NAb are expressed as medians [interquartile range (IQR)]. Frequencies of antibodies positivity 30 days after third dose and 30 days after fourth dose were compared using McNemar’s test. The mean of the neperian logarithm-transformed IgG titres and NAb activity were compared between timepoints (30 days after third dose and 30 days after fourth dose) using paired t-test. P < 0.05 are highlighted in bold. ARD: autoimmune rheumatic diseases; GMT: geometric mean titres (AU/mL).