In this Project we will monitor the symptoms of cat allergic participants who live together with a cat which is immunized with FEL-CMV using the novel symptom recording method "HypoScore", a General weekly symptom score, and a skin prick test before and after immunization of the cat. This project may enable us to determine if the scoring System and the tests are able to detect a difference in participant symptoms before and after immunization of the cats.

Inclusion Criteria:

• Signed informed consent after participants' information
• 18 to 65 years, male or female
• Participant understands the nature, meaning and scope of the study
• Positive screening prick test (wheal diameter ≥ 3mm) to Histamine dihydrochloride 10mg/ml
• Positive screening prick test (mean wheal diameter ≥ 3 mm) when tested with already standardized cat allergen extract
• Positive screening scratch test when tested with cat dander sample of participant's cat.
• Living with a cat in the same household and parallel participation in the cat study in which the cat will be immunized
• A positive clinical history with inhalant allergy presumably due to cat allergen

Exclusion Criteria:

• Immunosuppression or haematological diseases, in particular anaemias or leukaemia
• Other previous or current condition or participation in clinical trials influencing the results of the present study by discretion of the investigator
• Incapable of understanding the nature, meaning or scope of the research project or incapable of giving written informed consent
• Unwilling or incapable of following the study procedures, e.g. due to language problems, psychological disorders, dementia, known or suspected drug or alcohol abuse etc.
• Women who are pregnant or breast feeding or having the intention to become pregnant during the course of the study
• Positive skin reaction in the screening prick test to negative control
• History of anaphylactic reaction to pet allergens
• Severe diseases influencing the results of the present study by discretion of the investigator
• Immunotherapy with Fel d 1 / cat allergen preparation during the past two years.
• Skin lesions and excessive hair growth in the skin test areas
• Treatment with prohibited concomitant medications with the exception of medications with local effects which will not influence the results of the skin tests and the results of the other tests (testing period)
• The participant should not suffer from other respiratory allergies during this study (people who suffer from asthma are not excluded)