∙ Participants are eligible to be included in the study only if all of the following criteria apply:

∙ Informed Consent/Age

• Capable of giving signed informed consent as described in Appendix A which includes compliance with the requirements and restrictions listed in the ICF and in this protocol.

• Adult participants ≥ 18 years of age at the time of signing the ICF.

• Type of Participant and Disease Characteristics

• Participants must have clinical features of BP (eg, urticarial or eczematous or erythematous plaques, bullae, pruritus) at the screening visit and confirmed diagnosis with histology, direct immunofluorescence, and serology at randomization. Required for inclusion:

‣ Histology.

⁃ Positive direct immunofluorescence (from skin biopsy) (IgG and/or C3 at the basement membrane zone).

⁃ AND at least one of the following serologic assessments positive (all assessed from participant's blood sample):

• (i) indirect immunofluorescence (IgG on the roof of salt- split skin). (ii) positive serology on ELISA for BPAG1 (230-kd). (iii) positive serology on ELISA for BPAG2 (180-kd).

• BPDAI activity score ≥ 24 at the screening and randomization visits.

• Candidate for systemic corticosteroid therapy.

• Able to complete PRO assessments on a tablet and on a handheld device. Some participants may be exempted from completing home PROs on the handheld device upon agreement with the AstraZeneca physician (eg, if the patient has a medical condition such as BP lesions of the fingers/hand, a neurologic condition affecting fingers/hand, or severe visual impairment).

∙ Sex 7 Male or female.

∙ Reproduction 8 Female participants capable of having children must meet both of the following conditions (\[a\] and \[b\]):

∙ (a) Have a negative urine pregnancy test at screening and (b) Must agree to use a highly effective method of birth control (confirmed by the investigator) from randomization throughout the study duration and within 12 weeks after last dose of IP. Highly effective forms (those that can achieve a failure rate of less than 1% per year when used consistently and correctly) of birth control include: (i) Combined (estrogen and progestogen containing) hormonal contraception associated with inhibition of ovulation - oral, intravaginal, or transdermal.

∙ (ii) Progestogen-only hormonal contraception associated with inhibition of ovulation - oral, injectable, or implantable.

∙ (iii) Intrauterine device. (iv) Intrauterine hormone-releasing system. (v) Bilateral tubal occlusion. (vi) Sexual abstinence, ie, refraining from heterosexual intercourse (the reliability of sexual abstinence needs to be evaluated in relation to the duration of the clinical study and the preferred and usual lifestyle of the participant).

∙ (vii) Vasectomized sexual partner provided that partner is the sole sexual partner of the female of childbearing potential (FOCBP) study participant and that the vasectomized partner has received medical assessment of the surgical success.

∙ (c) Females not of childbearing potential are defined as females who are either permanently sterilized (hysterectomy, bilateral oophorectomy, or bilateral salpingectomy), or who are postmenopausal. Females will be considered postmenopausal if they have been amenorrhoeic for ≥ 12 months prior to the planned date of randomization without an alternative medical cause. The following age-specific requirements apply: (i) Females \< 50 years old will be considered postmenopausal if they have been amenorrhoeic for 12 months or more following cessation of exogenous hormonal treatment and follicle-stimulating hormone (FSH) levels in the postmenopausal range. Until FSH is documented to be within menopausal range, treat the participant as a female of childbearing potential.

∙ (ii) Females ≥ 50 years old will be considered postmenopausal if they have been amenorrhoeic for 12 months or more following cessation of all exogenous hormonal treatment.