A Study to Evaluate the Efficacy and Safety/Tolerability of Subcutaneous SCH 900222/MK-3222 in Participants With Moderate-to-Severe Chronic Plaque Psoriasis (P07771/MK-3222-011)

The base study consists of a screening phase of up to 4 weeks followed by a treatment period
of 52 weeks, and a 20-week follow-up period. The base study is divided into 3 sequential
parts.

In Part 1 of the base study (Week 0 to Week 12), participants will be randomized to one of 4
study arms (Arm A: MK-3222 200 mg + matching placebo to etanercept; Arm B: MK-3222 100 mg +
matching placebo to etanercept; Arm C: Matching placebo to MK-3222 + matching placebo to
etanercept; Arm D: Matching placebo to MK-3222 + etanercept 50 mg).

In Part 2 of the base study (Week 12 to Week 28), participants in Arm A and Arm B will
receive matching placebo to MK-3222 to maintain blinding at Week 12 and will receive either
MK-3222 200 mg (Arm A) or MK-3222 100 mg (Arm B) at Week 16. Participants in Arm A and Arm B
will also receive matching placebo to etanercept once weekly through study Week 28. At study
Week 12, Arm C participants will be re-randomized to receive their first dose of MK-3222 200
mg or MK-3222 100 mg, and will receive additional doses of study medication according to
their re-randomized treatment assignment at Week 16. Participants in Arm C will also receive
matching placebo to etanercept through treatment Week 28. Participants in Arm D will
continue with once weekly doses of etanercept through study Week 28 in combination with
matching placebo to MK-3222.

In Part 3 of the base study (Week 28 to Week 52), participants in Arm A with >= PASI-75
response at Week 28 will be re-randomized to either continue MK-3222 200 mg or receive
MK-3222 100 mg at study Weeks 28, 40, and 52. Participants with >= Psoriasis Area
Sensitivity Index of 50% (PASI-50) response but < PASI 75% (PASI-75) response will continue
to receive MK-3222 200 mg every 12 weeks and those participants with < PASI-50 response will
be discontinued from the study. Participants in Arm B with >= PASI-75 response at Week 28
will continue to receive MK-3222 100 mg every 12 weeks. Those with >= PASI-50 response but <
PASI-75 response will be re-randomized to receive continued MK-3222 100 mg or MK-3222 200 mg
every 12 weeks. Participants in Arm B with < PASI-50 response will be discontinued from the
study. Participants in Arm C will continue to receive treatment every 12 weeks according to
their re-randomized treatment assignment. Participants in Arm D that achieve >= PASI-75
response at Week 28 will be discontinued from the study. Those participants with < PASI-75
response at Week 28 will be crossed over to MK-3222 200 mg to receive doses at Week 32, Week
36, and Week 48.

Eligible participants that choose to enroll in the extension study will have an additional
treatment period of up to 192 weeks and will be followed for an additional 20 weeks in the
follow-up period. Each participant will receive MK-3222 200 mg or MK-3222 100 mg every 12
weeks up to study Week 244 according to their treatment assignment at the conclusion of Part
3 of the base study.

Inclusion Criteria:

- Clinical diagnosis of moderate-to-severe plaque psoriasis for at least 6 months prior
to enrollment;

- Candidate for phototherapy or systemic therapy;

- Premenopausal female participants must agree to abstain from heterosexual activity or
use a medically approved method of contraception or use appropriate effective
contraception as per local regulations or guidelines

- For the extension study: must have completed Part 3 of the base study

- For the extension study: must have achieved at least a PASI-50 response by the end of
Part 3 of the base study

Exclusion Criteria:

- Non-plaque forms of psoriasis

- Presence or history of severe psoriatic arthritis and is well-controlled on current
treatment regimen

- Women of childbearing potential that are pregnant, intend to become pregnant, or are
lactating

- Participant is expected to require topical therapy, phototherapy, or systemic therapy

- Presence of any infection or history of recurrent infection requiring treatment with
systemic antibiotics

- Previous use of MK-3222/SCH 900222, or other interleukin-23 (IL-23)/T- helper cell 17
(Th-17) pathway inhibitors including P40, P19, and IL-17 antagonists, or etanercept

- Latex allergy or sensitivity

- Active or untreated latent tuberculosis (TB)

- For the extension study: women of child-bearing potential that are pregnant, intend
to become pregnant within 6 months of completing the trial, or that are breast
feeding

- For the extension study: active or uncontrolled significant organ dysfunction or
clinically significant laboratory abnormalities

- For the extension study: expected to require topical treatment, phototherapy, or
systemic treatment during the extension study