Participants will receive starting dose of 160 milligrams (mg) 608 at week 0 followed by 80mg 608 once every two weeks (Q2W) by subcutaneous injection during induction period (12 weeks). During the maintenance period, participants will receive 80mg 608 once every four weeks (Q4W).

Participants will receive 160mg 608 once every four weeks (Q4W) by subcutaneous injection during induction period (12 weeks) followed by 160mg 608 once every eight weeks (Q8W) during maintenance period.

Participants will receive Placebo by subcutaneous injection during induction period and then, will be re-randomized to either receive starting dose of 160mg 608 at week 12 followed by 80mg 608 once every four weeks (Q4W) or 160mg 608 once every eight weeks (Q8W) during maintenance period.

608 160 mg at week 0 + 80 mg Q2W ( 6 cycles) +80 mg Q4W during maintenance period

The PASI combines the extent of body surface involvement in 4 anatomical regions (head, trunk, arms, and legs). For each region the percent area of skin involved was estimated from 0 (0%) to 6 (90%-100%) and severity was estimated by clinical signs of erythema, induration and scaling with a scores range from 0 (no involvement) to 4 (severe involvement). Each area is scored by itself and the scores then combined for the final PASI. Final PASI calculated as: sum of severity parameters for each region * area score * weighing factor [head (0.1), upper limbs (0.2), trunk (0.3), lower limbs(0.4)]. Overall scores range from 0 (no Ps) to 72 (the most severe disease).

The sPGA is the physician's determination of the participant's Ps lesions overall at a given time point. Lesions were categorized by descriptions for induration, erythema, and scaling. Participants Ps were assessed as 0 (clear), 1 (minimal), 2 (mild), 3 (moderate), 4 (severe), or 5 (very severe). An sPGA responder was defined as having a postbaseline sPGA score of "0" or "1" with at least a 2-point improvement from baseline.

The PASI combines the extent of body surface involvement in 4 anatomical regions (head, trunk, arms, and legs). For each region the percent area of skin involved was estimated from 0 (0%) to 6 (90%-100%) and severity was estimated by clinical signs of erythema, induration and scaling with a scores range from 0 (no involvement) to 4 (severe involvement). Each area is scored by itself and the scores then combined for the final PASI. Final PASI calculated as: sum of severity parameters for each region * area score * weighing factor [head (0.1), upper limbs (0.2), trunk (0.3), lower limbs(0.4)]. Overall scores range from 0 (no Ps) to 72 (the most severe disease).