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Thiomersal Vaccination — SCE Dermatology MCQ

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HardInflammatory DermatosesThiomersal VaccinationSCE Dermatology

Patch testing shows delayed contact sensitivity to thiomersal, but the patient has never had an immediate reaction to a vaccine. She is due routine immunisation. What should be advised?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: A — Proceed with the indicated vaccine; delayed contact sensitivity does not imply systemic allergy

Explanation lettering: B = shown as A · E = shown as B · A = shown as C · C = shown as E

B is correct. Delayed contact allergy does not predict IgE-mediated anaphylaxis to injected vaccine, and thiomersal is no longer routinely used in childhood vaccines in the UK. The product excipients and any genuine previous systemic reaction should still be reviewed, but a positive patch test alone is not a reason to withhold protection. Live status does not determine thiomersal content, universal graded challenges are unnecessary, and sensitisation is not managed by waiting for a negative repeat patch test.

Reference: UK Green Book chapter 8: vaccine safety: https://www.gov.uk/government/publications/vaccine-safety-and-adverse-events-following-immunisation-the-green-book-chapter-8