Protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection of inactivated vaccines is not well characterized in people with comorbidities, who are at high risk of severe infection. We compared the risk of SARS-CoV-2 infection after complete vaccination with Sinopharm/BBIBP in people with comorbidities (e.g., autoimmune diseases, cardiovascular disease, chronic lung disease, and diabetes) with healthy individuals using a Cox-proportional hazard model. In July–September 2021, a total of 10 548 people (comorbidities, 2143; healthy, 8405) receiving the complete primary series of vaccination with Sinopharm/BBIBP in Bangkok, Thailand were prospectively followed for SARS-CoV-2 infection through text messaging and telephone interviewing for 6 months. A total of 295 infections from 284 participants were found. HRs (95% CI) of individuals with any comorbidities did not increase (unadjusted, 1.02 (0.77–1.36), P = 0.89; adjusted, 1.04 (0.78–1.38), P = 0.81). HRs significantly increased in the subgroup of autoimmune diseases (unadjusted, 2.64 (1.09–6.38), P = 0.032; adjusted, 4.45 (1.83–10.83), P = 0.001) but not in cardiovascular disease, chronic lung disease, or diabetes. The protection against SARS-CoV-2 infection of the Sinopharm vaccine was similar in participants with any comorbidities vs. healthy individuals. However, the protection appeared lower in the subgroup of autoimmune diseases, which may reflect suboptimal immune responses among these people.