Clinical presentation, associated factors, and course of cutaneous reaction after the booster dose of COVID-19 vaccination.

Purpose: A booster coronavirus disease 2019 (COVID-19) vaccination was proposed to preserve immunity and prevent new variants of the severe acute respiratory syndrome coronavirus 2 virus. The objectives of this study are to investigate clinical manifestations, associated factors and course of cutaneous reactions after the booster dose of COVID-19 vaccination, compared to the recommended 1st and 2nd doses.

Materials and methods: This retrospective cohort study was conducted at Siriraj Hospital, Bangkok. Adult patients who reported cutaneous reactions after COVID-19 vaccination from April 2021 to February 2022 were included. Data were collected from electronic medical records and analyzed.

Results: A total of 521 subjects with a median age of 38 years were included. Females predominated (80.2%). Most reactions were reported after receiving CoronaVac (49.1%) and ChAdOx1 nCoV-19 (46.3%). The injection site reaction was the most reported. Twenty-one patients reported rash after the 3rd booster dose, with messenger RNA vaccines in most cases. Patients in this group had significantly fewer injection site reactions compared to those with the 1st and 2nd vaccination (70.6% vs. 91.5%) with an increasing proportion of new-onset urticaria (17.6% vs. 5.4%, p=0.023). The rash after the 3rd booster vaccination tended to have a longer duration of reactions (p=0.001). Boosting with a vaccine different from the 1st dose may not affect the reaction. Age and sex did not affect booster rash. In this study, no serious cutaneous reactions were found.

Conclusion: Most adverse cutaneous reactions after COVID-19 vaccination are mild in severity, especially after booster vaccination, and should not discourage the benefits of getting vaccinated.