| Placebo (n = 109) n (%) | Certolizumab pegol 400 mg (n = 111) n (%) | |
| Any AEs | 63 (57.8%) | 84 (75.7%) |
| Intensity: | ||
| Mild | 43 (39.4%) | 62 (55.9%) |
| Moderate | 40 (36.7%) | 52 (46.8%) |
| Severe | 11 (10.1%) | 8 (7.2%) |
| Serious AEs | 3 (2.8%) | 8 (7.2%) |
| Cases/100 patient years* | 9 | 18 |
| Serious infections | 0 (0%) | 2 (1.8%) |
| Cases/100 patient years* | 0 | 4 |
| AEs leading to death | 0 (0%) | 0 (0%) |
| AEs leading to withdrawal | 2 (1.8%) | 5 (4.5%) |
*Number of new cases per 100 patient years, calculated as the number of patients with the event under consideration divided by total exposure (censored at the time of the first event for those with an event under consideration).