ABSTRACT
Purpose: The morphology and timing of cutaneous reactions after Coronavirus disease (COVID-19) vaccines have been well described; however, data on the rates and risk factors are limited. Therefore, this study aimed to measure the incidence of cutaneous adverse reactions (CARs) after COVID-19 vaccination in Thailand, describe the rash characteristics according to the doses or types of vaccine, and assess the risk factors for developing CARs. Patients and Methods: This was a prospective observational study of adults who received COVID-19 vaccination and provided informed consent. Cutaneous diagnoses were made by expert dermatologists with supporting skin biopsies, as needed. Data were analyzed using descriptive statistics and logistic regression to examine the independent risk of developing a CAR. Results: Between July 2021 and January 2022, 7505 participants were vaccinated. Vaccine-related CARs occurred in 92 patients with an overall risk of 1.2%. CARs occurred after the first (n=41), second (n=23), third (n=27), and fourth (n=1) doses. Among the 92, 75 (81%) developed CARs within 7 days and 61 (66%) resolved within 7 days. Urticaria, injection site reaction, and a delayed (≥ 3 days post vaccine) local reaction were the three most common CARs occurring in 59 cases (64%). In total, 51 (55%) patients received only symptomatic and supportive treatment. Underlying urticaria and psoriasis were the independent factors for developing a CAR: adjusted odd rations of 15.63 (6.02-40.57, p < 0.001) and 5.36 (1.57-18.36, p = 0.007), respectively. A total of 6/34 (17%) and 4/31 (12%) patients developed urticarial and psoriasis flare post vaccine. Our study found superficial perivascular and intraepidermal eosinophil infiltration, which may be unusual pathological findings in vaccine-induced pemphigus foliaceous. Conclusion: CARs after COVID-19 vaccination had a low incidence and were mostly mild in severity and transient in nature. Underlying urticaria and psoriasis were risk factors for CAR development.