AbstractFor persons with immediate allergic reactions to mRNA COVID‐19 vaccines, skin testing (ST) to the vaccine/excipients (polyethylene glycol[PEG] and polysorbate 80 [PS]) has been recommended, but has unknown accuracy. To assess vaccine/excipient ST accuracy in predicting all‐severity immediate allergic reactions upon re‐vaccination, systematic review was performed searching Medline, EMBASE, Web of Science, and the WHO global coronavirus database (inception‐Oct 4, 2021) for studies addressing immediate (≤4 h post‐vaccination) all‐severity allergic reactions to 2nd mRNA COVID‐19 vaccination in persons with 1st dose immediate allergic reactions. Cases evaluating delayed reactions, change of vaccine platform, or revaccination without vaccine/excipient ST were excluded. Meta‐analysis of diagnostic testing accuracy was performed using Bayesian methods. The GRADE approach evaluated certainty of the evidence, and QUADAS‐2 assessed risk of bias. Among 20 studies of mRNA COVID‐19 first dose vaccine reactions, 317 individuals underwent 578 ST to any one or combination of vaccine, PEG, or PS, and were re‐vaccinated with the same vaccine. Test sensitivity for either mRNA vaccine was 0.2 (95%CrI 0.01–0.52) and specificity 0.97 (95%CrI 0.9–1). PEG test sensitivity was 0.02 (95%CrI 0.00–0.07) and specificity 0.99 (95%CrI 0.96–1). PS test sensitivity was 0.03 (95%CrI 0.00–0.0.11) and specificity 0.97 (95%CrI 0.91–1). Combined for use of any of the 3 testing agents, sensitivity was 0.03 (95%CrI 0.00–0.08) and specificity was 0.98 (95%CrI 0.95–1.00). Certainty of evidence was moderate. ST has low sensitivity but high specificity in predicting all‐severity repeat immediate allergic reactions to the same agent, among persons with 1st dose immediate allergic reactions to mRNA COVID‐19 vaccines. mRNA COVID‐19 vaccine or excipient ST has limited risk assessment utility.