Oral Food Challenge After One to Two Doses of Omalizumab Treatment for Food Allergy

The goal of this clinical trial is to learn how quickly omalizumab begins to work in people with food allergy. The main question it aims to answer is: * Does omalizumab begin to work as early as 2 to 4 weeks after after starting treatment in people with food allergy? Researchers will compare each participant's food challenge results at baseline before starting omalizumab, 2 to 4 weeks after starting omalizumab, and 4 to 6 months after starting omalizumab treatment. Participants will: * Have a baseline food challenge before starting omalizumab. * Start omalizumab treatment as prescribed by the participant's doctor as part of regular clinical care. * Have food challenges 2 to 4 weeks after starting omalizumab and again 4 to 6 months after starting omalizumab. * Have skin prick testing and blood tests at study visits.