IntroductionTo assess the incidence and risk factors for breakthrough COVID-19 infection in a vaccinated cohort of patients with autoimmune rheumatic diseases (AIRDs) and determine whether antibodies to receptor binding domain of spike protein (anti-RBD) serve as a reliable predictor of susceptibility to such infections.MethodsPatients with AIRDs who had completed two doses of SARS-CoV2 vaccines were included and anti-RBD antibodies were determined 4–6 weeks post the second vaccine dose and stratified into good responders (GR) (>212 IU), inadequate responders (IR) (0.8–212 IU) and non-responders (NR) (<0.8 IU). Patients who had completed a minimum of 8 weeks interval after the second dose of vaccine were followed up every 2 months to identify breakthrough infections. All sero converted patients who had contact with COVID-19 were also analysed for neutralising antibodies.ResultsWe studied 630 patients of AIRDs (mean age 55.2 (±11.6) years, male to female ratio of 1:5.2). The majority of patients had received AZD1222 (495, 78.6%) while the remaining received the BBV152 vaccine. The mean antibody titre was 854.1 (±951.9), and 380 (60.3%) were GR, 143 (22.7%) IR and 107 (16.9%) NR.Breakthrough infections occurred in 47 patients (7.4%) at a mean follow-up of 147.3 (±53.7) days and were proportionately highest in the NR group (19; 17.75%), followed by the IR group (13; 9.09%) and least in the GR group (15; 3.95%). On log-rank analysis, antibody response (p<0.00001), vaccine(p=0.003) and mycophenolate mofetil (p=0.007) were significant predictors of breakthrough infections. On multivariate Cox regression, only NR were significantly associated with breakthrough infections (HR: 3.6, 95% CI 1.58 to 8.0, p=0.002). In sero converted patients with contact with COVID-19, neutralisation levels were different between those who developed and did not develop an infection.ConclusionBreakthrough infections occurred in 7.4% of patients and were associated with seronegativity following vaccination. This provides a basis for exploring postvaccination antibody titres as a biomarker in patients with AIRD.

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