Humoral SARS–CoV‐2 Vaccine Responses in Patients With Giant Cell Arteritis and Polymyalgia Rheumatica: Decay After Primary Vaccination and Effects of the Booster

Vaccination remains essential in preventing morbidity of SARS–CoV‐2 infections. We previously showed that >10 mg/day of prednisolone and methotrexate was associated with reduced antibody concentrations after primary vaccination in patients with giant cell arteritis (GCA) and polymyalgia rheumatica (PMR). This follow‐up study was undertaken to measure the decay of antibody concentrations and the immunogenicity of SARS–CoV‐2 booster vaccination. Patients with GCA/PMR included in the primary vaccination (BNT162b2 [Pfizer‐BioNTech] or ChAdOx1 [Oxford/AstraZeneca]) study were asked again to donate blood samples 6 months after primary vaccination (n = 24) and 1 month after booster vaccination (n = 46, BNT162b2 or mRNA1273). Data were compared to those of age‐, sex‐, and vaccine‐matched controls (n = 58 and n = 42, respectively). Multiple linear regression was performed with post‐booster antibody concentrations as dependent variable and post‐primary vaccination antibodies, prednisolone >10mg/day, and methotrexate use as predicting variables. Antibody concentrations decreased faster over time in GCA/PMR patients than in controls, which was associated with prednisolone treatment during primary vaccination. Post‐booster antibody concentrations were comparable between patients and controls. Antibody concentrations post primary vaccination, but not treatment during booster vaccination, were predictive for antibody concentrations post booster vaccination. These results indicate that the decay of humoral immunity after primary vaccination is associated with prednisolone treatment, whereas the subsequent increase after booster vaccination, was not. Patients with low antibody concentrations following primary vaccination remained at an immunogenic disadvantage after a single booster vaccination. This longitudinal study in GCA/PMR patients stresses the importance of repeated booster vaccination for patients with poor responses to primary vaccination.