Evaluation of the reliability, validity and practicality of 3 measures of acute pain in infants undergoing immunization injections.

There is a need to identify a primary measure of infant pain that can be used to assess pain in infants undergoing vaccine injections in order to facilitate vaccine outcomes research. The aim of the present study was to determine the reliability, validity and practicality of 3 measures of acute pain in infants; the Modified Behavioural Pain Scale (MBPS), Neonatal Infant Pain Scale (NIPS), and Face Legs Activity Cry Consolability Scale (FLACC). Five raters rated pain from videotapes in 120 infants aged 2-6 months undergoing vaccine injections that participated in a randomized controlled trial designed to compare pain responses between two vaccines, DPTaP-Hib vaccine and PCV vaccine. Inter-rater reliability coefficients for baseline and vaccine injections were all greater than 0.85. Cronbach's alpha ranged from 0.83 to 0.94. Construct validity was demonstrated for all measures by vaccine injection scores that were higher (p<0.001) than baseline scores and by PCV scores that were higher than DPTaP-Hib scores. Concurrent validity was demonstrated by bi-variate correlation coefficients that ranged from 0.84 to 0.92. Intra-rater reliability coefficients for scores obtained after a single viewing (simulating real time assessment) versus multiple viewings were ≥ 0.96. All measures demonstrated a significant difference in pain scores between the more painful (PCV) and less painful (DPTaP-Hib) vaccine for scores obtained after a single viewing. The majority of raters (4 out of 5) preferred the MBPS. Together, these results provide preliminary support for the MBPS as the primary outcome of pain during vaccine injections in infants.