This is a study to demonstrate the clinical efficacy and safety of the nanobody® sonelokimab administered subcutaneously (sc) compared with placebo in the treatment of adult participants with moderate to severe hidradenitis suppurativa.

Inclusion Criteria:

1. Participant is ≥18 years of age;
2. Participant has been diagnosed with hidradenitis suppurativa as determined by the investigator and has a history of signs and symptoms of hidradenitis suppurativa dating back at least 6 months prior to the Screening Visit;
3. Participant has a total abscess and/or inflammatory nodule (AN) count of ≥5;
4. Participant has hidradenitis suppurativa lesions present in ≥2 distinct anatomical areas, at least one of which must contain single or multiple fistulas (i.e., be Hurley Stage II or III);
5. Participant had an inadequate response to appropriate systemic antibiotics for treatment of hidradenitis suppurativa (or demonstrated intolerance to, or had a contraindication to, systemic antibiotics for treatment of their HS), in the investigator's opinion;
6. Participant must be, in the opinion of the investigator, at both the Screening Visit and study treatment initiation, a suitable candidate for treatment with adalimumab per approved local product information.

Exclusion Criteria:

1. Participants with known hypersensitivity to sonelokimab or any of its excipients;
2. Participants with known hypersensitivity to adalimumab or any of its excipients;
3. Participant has a draining fistula count of ≥20 at the Screening Visit;
4. Participant has any other active skin disease or condition that may, in the opinion of the investigator, interfere with the assessment of hidradenitis suppurativa;
5. Prior exposure to more than 2 biologic response modifiers;
6. Participant has a diagnosis of ulcerative colitis or Crohn's disease.