A 52-week, Randomised, Double-blind, Placebo-controlled, Parallel-group, Multi-centre Study of the Efficacy and Safety of GSK3511294 Adjunctive Therapy in Adult and Adolescent Participants With Severe Uncontrolled Asthma With an Eosinophilic Phenotype

• Adults and adolescents greater than or equal to (\>=)12 years of age, at the time of signing the informed consent/assent.

• Participants must have a documented physician diagnosis of asthma for \>=2 years that meets the National Heart, Lung, and Blood Institute (NHLBI) guidelines or Global Initiative for Asthma (GINA) guidelines and

‣ Have, or with high likelihood of having, asthma with an eosinophilic phenotype

⁃ Have previously confirmed history of \>=2 exacerbations requiring treatment with systemic corticosteroid (CS) (intramuscular \[IM\], intravenous \[IV\], or oral), in the 12 months prior to Visit 1, despite the use of medium to high-dose ICS. For participants receiving maintenance CS, the CS treatment for the exacerbations must have been a two-fold dose increase or greater.

• Persistent airflow obstruction as indicated by:

‣ For participants \>=18 years of age at Visit 1, a pre-bronchodilator FEV1 less than (\<)80% predicted (The Third National Health and Nutrition Examination Survey \[NHANES III\]) recorded at Visit 1

⁃ For participants 12-17 years of age at Visit 1:

• A pre-bronchodilator FEV1 \<90% predicted (NHANES III) recorded at Visit 1 OR

∙ FEV1:Forced Vital Capacity (FVC) ratio \<0.8 recorded at Visit 1.

• A well-documented requirement for regular treatment with medium to high dose ICS (in the 12 months prior to Visit 1 with or without maintenance OCS). The maintenance ICS dose must be \>=440 micrograms (mcg) Fluticasone propionate (FP) Hydrofluoroalkane (HFA) product daily, or clinically comparable (GINA). Participants who are treated with medium dose ICS will also need to be treated with LABA to qualify for inclusion.

• Current treatment with at least one additional controller medication, besides ICS, for at least 3 months (for example \[e.g.\], LABA, LAMA, leukotriene receptor antagonist \[LTRA\], or theophylline).

⁃ Key randomization inclusion criteria:

• For blood eosinophilic count:

‣ An elevated peripheral blood eosinophil count of \>=300 cells/microliter (mcL) demonstrated in the past 12 months prior to Visit 1 that is related to asthma OR

⁃ An elevated peripheral blood eosinophil count of \>=150 cells/mcL at Screening Visit 1 that is related to asthma.

• Evidence of airway reversibility or responsiveness as documented by either:

‣ Airway reversibility (FEV1\>=12% and 200 milliliters \[mL\]) demonstrated at Visit 1 or Visit 2 using the Maximum Post Bronchodilator Procedure OR

⁃ Airway reversibility (FEV1\>=12% and 200 mL) documented in the 24 months prior to Visit 2 (randomization visit) OR

⁃ Airway hyperresponsiveness (methacholine: Provocative concentration causing a 20% fall in FEV1 \[PC20\] of \<8 milligrams (mg)/mL, histamine: PD20 of \<7.8 micromoles, mannitol: decrease in FEV1 as per the labelled product instructions) documented in the 24 months prior to Visit 2 (randomization visit).