Asthma is a chronic condition affecting approximately 5-15% of all Swedish children. Research has shown that asthma may be associated with increased anxiety and worry, with children who have asthma being twice as likely to experience anxiety compared to those without asthma. The coexistence of anxiety and asthma can worsen asthma symptoms and heighten anxiety, as it can be challenging to distinguish between the two conditions. Cognitive behavioral therapy (CBT) is a recommended treatment for anxiety in children, but few studies have examined the effectiveness of CBT in children with both asthma and anxiety. Our research group has previously developed internet-delivered CBT (Internet-CBT) targeting anxiety in asthma for adults, yielding promising results. Internet-CBT can significantly improve access to treatment and has been shown to be both effective and safe for other medical conditions.

The primary aim of this project is to investigate whether Internet-CBT can contribute to improved quality of life, better asthma control, and reduced anxiety in children and adolescents whose asthma is complicated by their own or their parents' anxiety. We have previously developed Internet-CBT for adults with asthma and anxiety with promising outcomes. For this study, we have adapted the treatment for children, adolescents, and their parents and will evaluate its feasibility and clinical effectiveness.

This study will use an uncontrolled pretest-posttest design, all participants will receive the intervention. The intervention consists of 8 weekly modules delivered over internet with guided support from an experienced CBT-trained psychologist.

Assessments will be made pretreatment, weekly during treatment for the primary outcome and potential mediators, posttreatment, at the primary endpoint 2 months after treatment completion and at follow up 6 months after treatment completion. Thirty participants (aged 8-17 years) will be included. All outcome data will be collected digitally and include for feasibility: treatment credibility, working alliance, compliance with the treatment (number of modules completed) and with asthma medications as prescribed by the child´s physician, any adverse events, subjective overall relief and satisfaction with treatment. For potential efficacy, the clinical effect in the group will be analyzed on pre- to post-measurements, including weekly measurements and 2 months follow up after treatment termination (primary endpoint). The participants will be followed 6 months after treatment completion to analyze longer term clinical effects.

Recruitment and inclusion procedure Participants will be self-recruited through advertisements in social media and posters at pediatric health care clinics. Potential participants will undergo an online self-report screening of eligible criteria. The parents and adolescents 15 and older, will receive digital information about the study and leave their written consent online. The screening will be followed by an evaluation with a clinical psychologist using a structured interview based on the DSM diagnostic. During the clinical interview, the children (>age 15) will receive information about the study and leave their informed consent orally. The families will have the opportunity to ask questions about the study and confirm previous written consent.

After inclusion, participants may start their treatment immediately.

Inclusion Criteria:

• Age 8-17 years
• A diagnosis of asthma made by a physician and confirmed by the parents
• Some anxiety related to asthma reported by either parent of child ("Do you feel stressed or worried about your asthma?" yes/no) and/or some restriction by asthma in daily life, which could indicate a pattern of avoidance behavior ("Do you feel hindered by your asthma in your daily life?" yes/no)

Exclusion Criteria:

• Presence of severe psychiatric disorders such as severe depression or suicidal ideation.
• Concurrent psychological treatment
• Presence of severe somatic disorder that could interfere with participation in the CBT-treatment
• Other respiratory disease than asthma
• Psychotropic medication should be stable for at least 1 month before entering the study.