In patients with systemic autoimmune rheumatic disorders (SARDs), vaccination with SARS-CoV-2 mRNA vaccines has been proposed. The aim of this study is to evaluate the immune response elicited by vaccination with mRNA vaccine, testing IgM, IgA and IgG antibodies to SARS-CoV-2 receptor-binding domain (RBD) and measuring neutralising antibodies.

IgG, IgM and IgA anti-RBD antibodies were measured in 101 patients with SARDs. Antibodies inhibiting the interaction between RBD and ACE2 were evaluated. Antibody avidity was tested in a chaotropic ELISA using urea. Twenty-one healthcare workers vaccinated with mRNA vaccine served as control group.

Anti-RBD IgG and IgA were produced after the first dose (69% and 64% of the patients) and after the boost (93% and 83%). Antibodies inhibiting the interaction of RBD with ACE2 were detectable in 40% of the patients after the first dose and 87% after boost, compared with 100% in healthy controls (p<0.01). Abatacept and mycophenolate had an impact on the titre of IgG anti-RBD antibodies (p<0.05 and p<0.005, respectively) and on the amount of neutralising antibodies. No effect of other therapies was observed. Vaccinated patients produce high avidity antibodies, as healthy controls.

These data show that double-dose vaccination induced in patients with SARDs anti-RBD IgG and IgA antibodies in amounts not significantly different from controls, and, most interestingly, characterised by high avidity and endowed with neutralising activity.