SHBC1149

X.R.LIM¹, J.W.L.TAN¹, G.Y.L.CHAN¹, S.C.TAN¹, S.S.M.LEE¹, J.F.HOU¹, L.L.XIE¹, V.H.L.GOH¹, K.P.LEONG¹, B.Y.H.THONG¹

Tan Tock Seng Hospital¹

Since the rollout of the Singapore’s national coronavirus disease 2019 (COVID-19) vaccination programme, there were 42 cases of anaphylaxis reported nationally amongst 5,470,425 doses of mRNA vaccines administered.

Patients with anaphylaxis defined by the Brighton Collaborative Case (BCC) Definition, seen by the Tan Tock Seng Hospital (TTSH) Allergy service were enrolled in our study of allergic reactions post COVID-19 vaccine from January to 30 June 2021. Data collected included patient demographics, atopy history, details of reaction, treatment administered and clinical course.

There were 7 patients (6 female) with anaphylaxis, all fulfilling definite/probable BCC criteria. 5 reactions occurred after the first dose and 2 after the second dose of the vaccine. The median age was 40 years (interquartile range 6), all with a history of atopy. Median interval from vaccine receipt to symptom onset was 20 minutes. The most common symptoms and signs were urticaria, angioedema, globus sensation and wheezing. Only 1 suffered from hypotension. Two were discharged after observation in the emergency department, while the rest were hospitalized for 2 to 4 days. Three required repeated doses of intramuscular adrenaline, with 1 patient suffering a triphasic reaction occurring 8 and 27 hours post vaccine administration. All recovered with 4 reporting prolonged urticaria post vaccination lasting 3 days to 6 months.

Clinicians should be made aware of the possibility of symptom recurrence and biphasic or triphasic reactions post mRNA vaccination. Our current national monitoring guidelines to observe vaccinees for 30 minutes post vaccination would pick up majority of the anaphylactic reactions.