In the double blind phase eligible patients will be randomized via an Interactive Voice Response System (IVRS) in a 1:1 ratio to receive either certolizumab pegol (400 mg at Weeks 0, 2 and 4, followed by 200 mg every two weeks) or placebo up to and including Week 22. All patients will continue to receive their Disease Modifying AntiRheumatic Drugs (DMARDs) therapy established before study entry until Week 52. At Week 24, patients will not receive any injection but will be evaluated: