Inclusion Criteria:  Male or female aged ≥18 years on the day informed consent is obtained A clinical history of grass pollen-induced allergic rhinoconjunctivitis for two years or more with or without asthma A clinical history of severe allergic rhinoconjunctivitis symptoms (interfering with usual daily activities or sleep) induced by grass pollen, which remain troublesome despite symptomatic treatment with antihistamines, nasal steroids or eye drops during the previous grass pollen season Positive specific immunoglobulin E (IgE) (defined as ≥class 2, ≥0.70 kU/l) against grass: Phleum pratense Positive skin prick test to Phleum pratense at screening  Exclusion Criteria:  Has a clinically relevant history of symptomatic seasonal and/or perennial allergic rhinoconjunctivitis and/or asthma caused by an allergen other than grass pollen, to which the subject is exposed, which could potentially overlap with the efficacy assessment periods Within the last 3 months before the randomisation visit, has had an occurrence of any clinical deterioration of asthma that resulted in emergency treatment, hospitalisation, or treatment with systemic corticosteroids SLIT treatment with any grass pollen AIT for more than 1 month within the last 5 years. In addition, any SLIT treatment with grass pollen AIT within the previous 12 months SCIT treatment with any grass AIT reaching the maintenance dose within the last 5 years. In addition, any SCIT treatment with grass AIT within the previous 12 months Ongoing treatment with any allergy immunotherapy product Uncontrolled or severe asthma requiring daily use of more than 800 mcg budesonide or equivalent at screening