Lost of sensitivity to diphteria-tetanus vaccine over time

Abstract Rationale In 2002, after an outbreak of meningococcal disease, massive vaccination with Menjugate® was implemented for all children of Quebec province. Because Menjugate® vaccine is conjugated to diphtheria protein, diphtheria-tetanus (DT) vaccine allergic children were skin tested with Menjugate® vaccine before vaccination. DT vaccine skin tests were repeated at the same time. Method Intradermal skin tests with DT vaccine were first performed with a 1/100 dilution. If negative, skin tests were repeated with a 1/10 dilution. Skin tests were considered positive if significant wheal (≥3mm) and/or flare (≥5mm) were present. Results Six DT vaccine allergic children lost their sensitivity over time. Previous allergic reactions for each child were: vomiting and dyspnea within 6 hours; whole limb swelling/erythema within 4 hours; generalized urticaria within 24 hours; maculopapular rash within 24 hours; vomiting, hypotonia and pallor within 3 hours; and generalized urticaria within 3 days. All had positive skin tests to DT vaccine on their first evaluation (five with a 1/100 dilution, one with a 1/10 dilution). All had negative skin tests to DT vaccine when repeated. Median age at allergic reaction was 5 months (range 2-18 months). Median age at first test was 27 months (range 12-64 months). Median time interval between testing was 43 months (range 21 months-16 years). All children tolerated DT revaccination after their skin tests negativated. Conclusion DT vaccine sensitivity can be lost over time. Vaccine skin tests should be repeated on vaccine allergic individuals in order to document possible lost of sensitivity and therefore resume vaccination.