• Participants who have signed and dated Informed Consent Form (ICF).

• Female or male aged 12 to 65 years, both included, at the time of signature of ICF.

• Participants with confirmed clinical history of inhalation allergy with intermittent or persistent moderate-severe rhinitis/ rhinoconjunctivitis according to the ARIA classification(1) of at least 1 year of duration (treated with anti-allergic medication) with or without mild-moderate controlled intermittent or persistent asthma according to the definition of GINA 2022(2) caused by Dermatophagoides pteronyssinus and/or Dermatophagoides farinae.

• Participants with positive skin prick test and a wheal major diameter ≥ 5 mm to a standardized allergen extract of Dermatophagoides pteronyssinus and/or Dermatophagoides farinae.

• Women of childbearing age (i.e., following menarche and until postmenopause, defined as no menses for 12 months without an alternative medical cause, or non-subject to permanent sterilisation methods, such as hysterectomy, bilateral salpingectomy and bilateral oophorectomy) must have a serum pregnancy test negative result, and a confirmed menstrual period before enrolling the study.

• Women of childbearing age must commit to using a highly effective contraception method during the trial and up to 1 month after the end of treatment with the investigational medicinal product (IMP). Such methods include: combined (estrogen and progestogen containing) hormonal, contraception. associated with inhibition of ovulation (oral, intravaginal or transdermal), progestogen-only hormonal contraception associated with inhibition of ovulation (oral, injectable or implantable), intrauterine device, intrauterine hormone-releasing system, male condom, diaphragm used with spermicide, bilateral tubal occlusion, vasectomized partner or sexual abstinence.

• Participants capable of complying with dosage regimen.

• Participants owning a smartphone to register symptoms and medication consumption.

• Participants not sensitized to any other clinically relevant allergen or sensitized with the following characteristics (sensitization to other allergens will be assessed through skin prick test in Europe and LATAM and through IgE levels in China):

∙ Participants sensitized to dander (with a positive skin prick test for dander or IgE ≥ 0.35 kU/L), provided that they have occasional exposure and symptoms.

‣ Participants sensitized to endemic pollen (with a positive skin prick test or IgE ≥0.35 kU/L) will be scheduled to be included so that the pollen season does not coincide with the Baseline Evaluation Period nor with one month before and after the Main Evaluation Period. In LATAM, grass sensitized participants will not be included.

⁃ Participants not sensitized to moulds, cockroach, Blomia tropicalis or other geographically relevant mites (negative skin prick test or IgE \< 0.7 kU/L).

⁃ Participants with a RCSMS ≥ 3 out of 6 recorded for at least 10 days during the baseline evaluation period, corresponding to moderate-to-severe allergic rhinitis/rhinoconjunctivitis.

⁃ Participants with specific IgE against a complete extract of D. pteronyssinus and / or D. farinae or any of the molecular components of allergenic sources with a value ≥ 3.5kU/L.