Efficacy and Safety Study of Guselkumab in the Treatment of Participants With Active Psoriatic Arthritis (PsA)

This is a multi-center (more than one clinical site will work on a medical research study), randomized (study medication assigned to participants by chance), double-blind (neither investigator nor participant knows which treatment the participant receives), placebo-controlled (placebo is an inactive substance that is compared with a drug to test whether the drug has a real effect in a clinical trial) study to determine the efficacy and safety of guselkumab in participants with PsA. The study will consist of 4 parts: Screening period (6 weeks), a double-blind treatment period (consists of guselkumab and placebo treatment for 24 weeks), an active treatment period (guselkumab for 20 weeks), and follow-up period (12 weeks). The maximal study duration for a participant will not exceed 62 weeks including the Screening period. Eligible participants will be randomly assigned to one of two groups in a 2:1 ratio to either receive Guselkumab 100 milligram (mg) at Weeks 0, 4 then every 8 weeks or Placebo at Weeks 0, 4 then every 8 weeks until Week 24. At week 24, participants remaining in the placebo group will start to receive guselkumab 100 mg at Weeks 24, 28, 36 and 44. Participants in both treatment groups who have less than (\<) 5 percent (%) improvement from baseline in both tender and swollen joint counts at Week 16 will qualify for early escape and will switch to open-label therapy with ustekinumab 45 mg or 90 mg at Weeks 16, 20, 32, and 44 based on the approved dosage for the PsA indication in the particular country of study. The efficacy will be assessed primarily by measuring percentage of participants who achieve an American College of Rheumatology (ACR) 20 Response at Week 24. Participants' safety will be monitored throughout the study.