LAUSR

Coronavirus disease 2019 (COVID19) is a global pandemic. Vaccines serve as a key factor in overcoming this serious disease. Since COVID19 vaccines are brand new, unexpected side effects are a serious concern, and fear of side effects leads to abstinence from vaccination. Syncope is defined as the sudden onset of loss of consciousness with collapse and prompt recovery with a possible connection to serious adverse outcomes. Syncope is a common adverse symptom of vaccination.1 The prevalence of syncopal episode after COVID19 vaccination has been reported,2 however, the precise incidence rate and a typical adolescent case with detailed presentation on COVID19 vaccineinduced syncope have not been published to the best of our knowledge. As COVID19 vaccination has recently begun in adolescents in Japan, this information would be useful. We present two typical cases of vasovagal (reflex) syncope in adolescent patients who received the COVID19 vaccine manufactured by Pfizer in a consecutive cohort, and we discuss the clinical features and the incidence of syncope caused by vaccination by comparing it with other vaccinations. Written informed consent was obtained from the following patients. Case 1: A 19yearold healthy man received his first dose of the Pfizer COVID19 vaccine, and he fainted 17 min after the vaccine injection without prodrome when he stood up and started to walk after 15 min of waiting at the hall for observation. The patient suddenly lost consciousness and collapsed on the floor. After lying on the floor, he promptly responded to auditory stimuli, and his consciousness returned to normal. His blood pressure was 90/60 mmHg, and his pulse rate was 49 bpm. Intravenous atropine sulfate of 0.5 mg was administered. His consciousness fully recovered, with a normal 12lead electrocardiogram. His blood tests, including those examining AST, ALT, CPK, CRP, troponin T, Ddimer, and complete blood counts, were within normal limits. Case 2: An 18yearold healthy woman passed out at the hall while waiting for 10 min after the first dose of the Pfizer COVID19 vaccine. She suddenly collapsed and lay down on the floor without any prodrome. She was dazed but responded well. Her blood pressure was 84/58 mmHg, and her pulse rate was 58 bpm and regular, with a normal 12lead electrocardiogram. Her blood tests and complete blood count results were normal. Intravenous normal saline (500 ml) was rapidly administered and her consciousness fully recovered. In our institute, 10 421 Pfizer COVID19 vaccinations were performed until October 10, 2021. We encountered two patients with syncope that we believe were associated with the vaccination. The calculated prevalence of syncope rate of Pfizer COVID19 vaccination was 0.019%, whereas we reviewed the medical records in our institute for the past 5 years and found no syncope or presyncope among 10 246 influenza vaccinations. Our two patients showed typical conditions of vaccineinduced syncope which is associated with fear and anxiety caused by vaccine injection,1 and reflex syncope is diagnosed. Even if reflex syncope was expected, medical emergency treatments were