Introduction and importanceKounis syndrome, also known as allergic angina syndrome, is defined as the occurrence of an acute coronary syndrome concomitantly with a hypersensitivity reaction. It is a very important diagnosis and missing it may be fatal to the patient. This is a medical emergency, and immediate treatment should be initiated. The treatment of Kounis syndrome is challenging because treatment of either acute coronary syndrome and hypersensitivity reaction can lead to the worsening of the other injury. This case is the first reported case of Kounis syndrome following coronavirus disease 2019 vaccination in Sri Lanka according to our knowledge.Case presentationWe discuss a 54-year-old female Sri Lankan patient who developed Kounis syndrome following Oxford AstraZeneca COVID-19 vaccination. The patient initially developed anaphylaxis following the AstraZeneca COVID-19 vaccine and subsequently developed acute coronary syndrome secondary to anaphylaxis. The patient was treated appropriately and eventually recovered from her condition.ConclusionThis syndrome should be suspected when there is a concurrent acute coronary syndrome with allergic reactions. This is an often under- or misdiagnosed condition, and physicians should be educated about it. Caregivers should be aware of its pathophysiology, as treatment of either of the two may worsen the other injury.