Background: Differences in pain response to two different M-M-R products have previously been demonstrated in 12-month old infants and in 4 â 6 year old children. Objective To determine if the acute and immediate pain response to two licensed M-M-R vaccine products (using a self-report measure) in children 4-6 years of age was similar to that demonstrated in younger infants.
Methods: Randomized, double blind, study. Subjects were randomly allocated to PriorixA (SmithKline Beecham) or M-M-R IIA (Merck Frosst). The primary outcome measure was pain response to vaccination quantified using a self-report OUCHER pain scale. Secondary outcome measures included pain measurement by proxy (physician and parent) using a visual analog scale (VAS) and measurement of cry and cry duration immediately post-vaccination.
Results: Of the 60 subjects enrolled, 30 received PriorixA and 30 received M-M-R IIA. There were no significant differences between the two groups on age, sex, or previous painful procedure. Post-vaccination, children in the M-M-R IIA group had higher median pain scores compared with children in the PriorixA group for VAS (12.5 vs. 2.0, respectively by paediatricians, p=0.017; 18.5 vs. 5.0, respectively by parents, p=0.235), OUCHER (20 vs. 0.00, respectively, p=0.047). The median duration of crying post M-M-R IIA was higher compared with PriorixA (6 vs. 0 seconds, respectively, p=0.020). Conclusion PriorixA was associated with significantly less pain compared with M-M-R IIA, at the time of injection.