An Efficacy, Safety, and Pharmacokinetics Study of Subcutaneously Administered Ustekinumab in the Treatment of Moderate to Severe Chronic Plaque Psoriasis in Pediatric Participants Greater Than or Equal to 6 to Less Than 12 Years of Age

The purpose of this study is to evaluate the efficacy and safety of ustekinumab in pediatric participants aged greater than or equal to (\>=) 6 through less than (\<) 12 years with moderate to severe chronic plaque psoriasis

This is an open label (identity of study drug will be known to participant and study staff) and multicenter (when more than one hospital or medical school team work on a medical research study) study. The participant population will be comprised of boys and girls who have had a diagnosis of plaque psoriasis for at least 6 months prior to first study drug administration and who have moderate to severe disease defined by Psoriasis Area and Severity Index score (PASI) \>=12, Physician's Global Assessment (PGA) \>=3, and Body Surface Area (BSA) \>=10 percent (%). The study consists of Screening Phase (up to 10 weeks before administration of the study drug), Treatment Period (Week 0 up to Week 52) and Safety follow up (Week 56). Participants will be primarily evaluated for efficacy, pharmacokinetics (PK) and safety. Following completion of the Week 52 visit, participants who have had a beneficial response from ustekinumab treatment as determined by the investigator, and who have not yet reached the age of 12 years or older in countries where marketing authorization for ustekinumab has been granted for the treatment of psoriasis in adolescent participants (12-17 years), and are willing to continue ustekinumab treatment, may enter the long-term extension period (from Week 56 through Week 264) of the study.

Eligibility Criteria:
Inclusion Criteria:

* Participants who have a diagnosis of plaque-type psoriasis with or without psoriatic arthritis (PsA) for at least 6 months prior to first administration of study drug, with widespread lesions defined by Psoriasis Area and Severity Index score (PASI) greater than or equal to (\>=) 12, Physician's Global Assessment (PGA) \>=3, and involved body surface area (BSA) \>=10 percent (%)
* Participants who are candidates for phototherapy or systemic treatment of psoriasis (either naive or history of previous treatment) or have psoriasis considered by the investigator as poorly controlled with topical therapy after an adequate dose and duration of therapy
* Participants who are considered eligible according to the protocol defined tuberculosis (TB) screening criteria
* Participants must have positive protective antibody titers to varicella and measles prior to the first administration of study drug. In the absence of positive protective antibody titers, the participant must have documentation of age-appropriate vaccination for varicella and/or measles (that includes both doses of each vaccine) or verification of past varicella and/or measles infection documented by a health care provider
* Participants must agree not to receive a live virus or live bacterial vaccination at least 2 weeks (or longer as indicated in the package insert of the relevant vaccine) prior to the first administration of study drug, during the study, or within 15 weeks after the last administration of study drug
* Participants must agree not to receive a Bacille Calmette-Guerin (BCG) vaccination within 12 months of screening, during the study, or within 12 months after the last administration of study drug

Exclusion Criteria:

* Participants who currently have nonplaque forms of psoriasis (example, erythrodermic, guttate, or pustular)
* Have received any systemic immunosuppressants (example methotrexate \[MTX\], azathioprine, cyclosporine, 6-thioguanine, mercaptopurine, mycophenolate mofetil, hydroxyurea, and tacrolimus) within 4 weeks of the first administration of study drug
* Have received any biologic agent (example ENBREL, HUMIRA) within the previous 3 months or 5 times the t1/2 of the agent, whichever is longer
* Have a history of chronic or recurrent infectious disease
* Have a history of latent or active granulomatous infection
* Have any known malignancy or have a history of malignancy
* Have a known history of lymphoproliferative disease, including lymphoma, or signs and symptoms suggestive of possible lymphoproliferative disease