A NEW METHOD FOR ACTIVE SURVEILLANCE OF ADVERSE EVENTS FROM DIPHTHERIA-TETANUS-PERTUSSIS AND MEASLES MUMPS RUBELLA VACCINES

We describe a new method for active post-marketing surveillance of vac cine safety based on patient records. We studied the association betwe en diphtheria/tetanus/pertussis (DTP) vaccination and febrile convulsi on, and between measles/mumps/rubella (MMR) vaccination and febrile co nvulsion and idiopathic thrombocytopenic purpura (ITP) in five distric t health authorities in England by linking vaccination records with co mputerised hospital admission records. We found an increased relative incidence for convulsions 0-3 days after DTP vaccination. The effect w as limited to the third dose of vaccine for which the attributable ris k (all ages) was 1 in 12 500 doses. Completion of vaccination by 4 mon ths instead of 10 months after the change in the UK to an accelerated immunisation schedule may have resulted in a 4-fold decrease in febril e convulsions attributable to DTP vaccine. 67% of admissions for a con vulsion 6-11 days after MMR vaccination were attributable to the measl es component of the vaccine (risk 1 in 3000 doses). An excess of admis sions for a convulsion 15-35 days after MMR vaccination was found only for vaccines containing the Urabe mumps strain (1 in 2600 Urabe doses ). There was a causal association between MMR vaccination and ITP resu lting in admission 15-35 days subsequently; there was no evidence of a mumps strain-specific effect. The estimated absolute risk of 1 in 24 000 doses was 5 times that calculated from cases passively reported by clinicians. This finding emphasises the need for active surveillance of adverse events. The record linkage method that we used is an effect ive way to identify vaccine-attributable adverse events.