Anti-S1/RBD-Specific Antibody Formation After SARS-CoV-2 Vaccination in Elderly Rheumatoid Arthritis Patients: Single-Center Prospective Observational Study

Background: The guidelines of coronavirus disease 2019 (COVID-19) vaccination in patients with rheumatoid arthritis (RA) have been continuously updated, with extensive discussion on the effectiveness of the COVID-19 booster vaccines and antibody generation associated with the different types of vaccine. We investigated the effects of the third dose of the mRNA vaccine on antibody titer and the factors associated with antibody production in patients with RA who had previously received two doses of the ChAdOx1-S nCoV-19 vaccine. Methods: Between October 14, 2021 and June 17, 2022, two patient groups diagnosed with RA were recruited prospectively: one with two doses of ChAdOx1-S nCoV-19 and the second group with the additional third mRNA vaccine. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody titers were determined through semiquantitative anti-SARS-CoV-2 spike (S) electrochemiluminescence immunoassay. Antibody titers were compared in both groups considering clinical features and medications. Multivariate logistic regression was performed to identify the factors associated with antibody production. Also, we followed up the antibody titers of whom completed the 3rd mRNA vaccination.Results: Among 261 patients, all patients were over 60 years old except for 7 patients and the average age was 65 years; 153 had completed two doses of ChAdOx1-S nCoV-19, while 108 patients had also received the third mRNA vaccine. The positive rates of anti-SARS-CoV-2 anti-S1/receptor binding domain-specific antibody (titer > 0.8 U/mL) were 97% (149/153) and 99% (107/108) respectively. However, positive rates for high antibody titer (> 250 U/ mL) were found in only 31% (47/153) of group 1 but 94% (102/108) of group 2. Multivariate analysis revealed that corticosteroid use (odds ratio [OR], 0.35; 95% confidence interval [CI], 0.16-0.75), older age (OR, 0.91; 95% CI, 0.860-0.98), and male sex (OR, 0.23; 95% CI, 0.07-0.74) were associated with a lower rate of high antibody titer acquisition after two doses of ChAdOx1-S nCoV-19. Waning of antibody titers was observed in only two of 46 patients who followed up twice after the third mRNA vaccine inoculation.Conclusion: Our findings suggest that the third dose of the mRNA vaccine could be beneficial in RA patients with risk factors including older age, male sex, and corticosteroid use after two doses of ChAdOx1-S nCoV-19.