Abstract
Omalizumab can cause hypersensitivity reactions. We herein report the first case of an 18-year-old woman with refractory cough-predominant asthma that correlated with allergic reactions caused by omalizumab and the coronavirus disease 2019 (COVID-19) vaccine. The patient developed angioedema after taking omalizumab. She had previously experienced intense coughing immediately after receiving a COVID-19 vaccine. A skin prick test was positive for polysorbate 20, which was probably the cause of the allergic reactions to omalizumab and the COVID-19 vaccine. Clinicians should check for an allergic reaction, irrespective of its intensity, triggered by polysorbate and be careful when prescribing biologics to patients in order to avoid allergic reactions.