BACKGROUND AND AIMS
Early studies have reported delayed injection-site reactions in up to 0.8% of individuals receiving Moderna messenger RNA (mRNA) vaccine.1 These are believed to be benign and do not contraindicate subsequent doses.2 Injection-site reactions after Pfizer-BioNTech mRNA vaccine have been less clearly described.3 This study reports the characteristics of mRNA COVID-19 injection-site reactions post-Moderna and Pfizer- BioNTech vaccinations.
MATERIALS AND METHODS
Patients referred to the authors’ dermatology service and allergy centre for reactions after COVID-19 vaccination between January 2021 and August 2021 were retrospectively reviewed. Inclusion criteria were adult patients who developed localised injection-site reactions after either Moderna or Pfizer-BioNTech mRNA vaccination. Patients with unrelated or non-injection site reactions were excluded. The data was analysed using IBM (Louisville, Kentucky, USA) SPSS Statistics version 22.0, with a p value of ≤0.05 being considered statistically significant.
Three hundred and twenty-two patients were referred for post-vaccination reactions, of which 21 developed injection-site reactions. Patients receiving Moderna mRNA vaccine had a longer median latency period (p=0.001), and were more likely to have a latency duration of >5 days (p=0.009). Secondary dissemination of the injection-site reaction was seen in both groups. More than half of these patients did not require any treatment. All 21 patients subsequently received the second vaccine dose, of which two (9.5%) developed a mild recurrence of the reaction that did not require treatment.
Delayed local injection-site reactions to both vaccines appear to be benign. All patients went on to receive the second dose despite the initial first dose reactions, with none developing severe allergic reactions. While the latency between vaccination and onset of cutaneous lesions is significantly shorter following Pfizer-BioNTech vaccination, it remains unclear if pathogenic mechanisms behind injection reactions across the two vaccines differ. With the call for booster vaccinations globally, it is important to recognise that these reactions are mild, self-limiting, and should not deter one from subsequent vaccines.