Can a pinpoint pollen dose unmask allergy triggers?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: 1. Able and willing to give written informed consent. 2. Male and female subjects, aged 18-65 years. Women will be considered for inclusion if they are: 1. Not pregnant, as confirmed by pregnancy test (see flow chart), and not nursing. 2. Of non-child bearing potential (i.e. physiologically incapable of becoming pregnant, including any female who is post-menopausal, with documented proof of hysterectomy or tubal ligation, or meets clinical criteria for menopause and has been amenorrhoeic for more than 1 year prior to the screening visit). 3. Of childbearing potential and using a highly effective birth control during the entire study as described in section 8.2. 3. Body mass index between 18 and 35 kg/m2. 4. History of seasonal allergic rhinitis to ragweed (July to September) or birch pollen (March to May). 5. Positive skin prick test response (positive wheal diameter reaction of ≥ 3mm) for Ambrosia artemisiifolia or Betula pendula at screening or within 12 months prior to screening visit. 6. Subject has a serum specific IgE level (≥ 0.7 kU/L) to Ambrosia artemisiifolia or Betula pendula at screening or within the past 12 months (record required). 7. Normal lung function (FEV1 ≥ 80% pred. and FEV1/FVC ≥ LLN) at screening. If subject fails to meet criteria, assessment may be repeated 2 additional times. 8. TNSS of 0 prior to entering the ACC at all exposures. 9. Mild to moderate level of rhinitis symptoms in the screening challenge to ragweed or birch, defined as a mean TNSS between 1 to 8 after the 4-hour ACC and a TNSS continuously \> 0 after 40 minutes. Exclusion Criteria: 1. Any clinically relevant abnormal findings in physical examination, clinical chemistry, hematology, urinalysis, vital signs, lung function or ECG at screening visit , which, in the opinion of the investigator, may either put the subject at risk because of participation in the study or may influence the results of the study, or the subject's ability to participate in the study. 2. Past or present disease, which as judged by the investigator, may affect the outcome of this study. These diseases include, but are not limited to, cardiovascular disease, malignancy, hepatic disease, renal disease, hematological disease, neurological disease, endocrine disease or pulmonary disease (including but not confined to chronic bronchitis, emphysema, tuberculosis, bronchiectasis or cystic fibrosis). 3. Subjects with concomitant allergies to seasonal aeroallergens (i.e., grass, trees, weeds, rye; defined as IgE ≥ 3.5 kU/L within the last 12 months prior to screening) which are anticipated to be or become active during study participation. 4. Subjects with a symptomatic concomitant allergy to an animal dander being exposed during study participation. 5. Subjects with a symptomatic house dust mite allergy. 6. Symptoms of a respiratory tract infection within 3 days prior to screening. Subjects may be re-screened if they have been asymptomatic for at least 3 days. 7. Asthma requiring more than Step 1 medication according to GINA guidelines (Global Initiative for Asthma Management and Prevention, 2021). Asthmatic subjects taking ICS plus long-acting bronchodilator as needed according to Step 1 must to be switched to salbutamol as needed during study participation. 8. Intake of prohibited medication (refer to Section 9.2). 9. Smokers who are unable to refrain from smoking within 1 hr prior to and during visits. 10. Anatomical nasal abnormalities, pronounced nasal septum deviation or nasal polyps blocking nasal air flow on examination or recent nasal surgery. 11. Participation in a clinical trial with a medicinal product or medical device 30 days prior to Visit 1. 12. History of drug or alcohol abuse in the past 12 months. 13. Specific Immunotherapy (SIT) against birch or ragweed within 5 years prior to the study. 14. Risk of non-compliance with study procedures. 15. Suspected inability to understand the protocol requirements, instructions and study-related restrictions, the nature, scope, and possible consequences of the study.