ABSTRACT
Background: To date, over 10 million doses of mRNA vaccines (BNT162b2 mRNA and mRNA-1273) have been administered in Singapore. Initial studies have shown that 0.8% of individuals who received Moderna mRNA vaccine developed delayed injection-site reactions. Reactions to the Moderna mRNA vaccine are thought to be benign and not a contraindication to further doses. Injection-site reactions associated with the Pfizer-BioNTech mRNA vaccine are less clearly defined. We report the characteristics of mRNA COVID-19 injection-site reactions, comparing the clinical features between Moderna (mRNA-1273) and Pfizer-BioNTech (BNT162b2) reactions in the Singaporean adult population. Method(s): We retrospectively reviewed patients referred to the Dermatology Service / Allergy Centre of a tertiary hospital in Singapore for reactions post COVID-19 vaccination between 10 Jan 2021 and 26 Aug 2021. Inclusion criteria were adult patients who developed a localised injection-site reaction after either Moderna or Pfizer-BioNTech mRNA COVID-19 vaccination. Result(s): 322 patients were referred for post-COVID- 19 vaccine reactions, of which 21 developed injection-site reactions. 11 (52%) had received the Moderna mRNA vaccine while 10 (48%) received the Pfizer-BioNTech mRNA vaccine. Patients receiving the Moderna mRNA vaccine had a longer mean latency period (p = 0.047) and were more likely to have a latency duration of > 5 days (p = 0.007). Secondary dissemination of the injection-site reaction was seen in 2 patients. 11 (52%) of these reactions resolved without treatment;while the remaining 10 (48%) required symptomatic treatment with topical corticosteroids, antihistamines, or a combination of both. All 21 patients subsequently received the second vaccine dose, of which 2 (9.5%) developed recurrence of the reaction;both of which were mild and did not require treatment. Conclusion(s): Localised injection-site reactions post Moderna or Pfizer-BioNTech mRNA COVID-19 vaccination are uncommon and appear to be phenotypically different. Such reactions are benign and self-limited. While recurrence of the reaction can arise during repeat vaccine doses, these are mild and self-limited.