ObjectiveTo date, the only study that has assessed the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2 mRNA) vaccine in systemic lupus erythematosus (SLE) observed a moderate response, but the sample size precluded an accurate analysis of the effect of individual drugs. Therefore, we evaluated the immunogenicity of an inactivated SARS‐CoV‐2 vaccine (Sinovac‐CoronaVac) and the influence of different medications in SLE. Safety was also assessed.MethodsWe conducted a prospective controlled study of 232 SARS‐CoV‐2–naive SLE patients and 58 SARS‐CoV‐2–naive controls who were vaccinated with 2 doses of Sinovac‐CoronaVac with a 28‐day interval (day 0/day 28 [D0/D28]). Immunogenicity analysis at D0/D28 and D69 included anti‐SARS‐CoV‐2 S1/S2 IgG seroconversion (SC) and neutralizing antibodies (NAb) positivity. The influence of individual drugs on immune response and safety was assessed.ResultsPatients and controls were well balanced for age (P = 0.771). At D69, SLE patients showed a moderate SC (70.2% versus 98.1%; P < 0.001) and moderate frequency of NAb positivity (61.5% versus 84.6%; P = 0.002), although both frequencies were lower than in controls. Factors associated with lower SC in univariate analysis at D69 were prednisone use (odds ratio [OR] 0.215 [95% confidence interval (95% CI) 0.108–0.427], P < 0.001) and mycophenolate mofetil (MMF) use (OR 0.201 [95% CI 0.107–0.378], P < 0.001), whereas hydroxychloroquine (HCQ) use led to a 2.5 increase in SC (P = 0.011). SLE patients who were receiving HCQ monotherapy had similar SC to controls at D69 (100% versus 98.1%; P = 1.000). In multivariate analysis, prednisone and MMF use were independently associated with lower SC (P < 0.001) and NAb positivity (P < 0.001). Safety analysis revealed no moderate/severe adverse events.ConclusionSinovac‐CoronaVac has a moderate immunogenicity in SARS‐CoV‐2–naive SLE patients with an excellent safety profile. We further demonstrate that HCQ may improve SC, whereas prednisone and MMF had a major deleterious effect in vaccine response, reinforcing the need to investigate the role of temporary MMF withdrawal or a vaccine‐booster dose (ClinicalTrials.gov identifier: NCT04754698).