A randomized trial of the effect of vaccine injection speed on acute pain in infants

Abstract

Objective: This study compared the pain caused from fast vs. slow vaccine injections.

Methods: Infants aged 2-6months receiving primary immunizations were randomized to fast (2-4mL/s) or slow (5-10mL/s) injections during routine 0.5mL Diphtheria, Tetanus, acellular Pertussis, Inactivated Polio Virus, Haemophilus influenzae type b vaccine (DTaP-IPV-Hib) injections. Those aged 2 and 4months additionally received 0.5mL Pneumococcal Conjugate Vaccine (PCV) injections. A research assistant and parent unaware of treatment allocation and hypothesis assessed pain using validated and recommended tools, including; the Modified Behavioural Pain Scale (MBPS, range 0-10), cry duration, and Numerical Rating Scale (NRS, range 0-10). The primary outcome was infant pain score using the MBPS.

Results: Altogether, 120 were recruited; 61 were randomized to fast injections and 59 to slow injections. One hundred and ninteen infants participated. There were no differences in characteristics, including; age (p=0.994) and sex (p=0.540). The mean MPBS score (standard deviation) during DTaP-IPV-Hib injection was lower in the fast injection group: 6.4 (2.7) vs. 7.4 (2.5), respectively; p=0.046. Regression analysis demonstrated a positive correlation between injection speed and pain. There were no other differences between groups.

Conclusion: Fast injection reduced injection-induced pain in infants receiving DTaP-IPV-Hib but not PCV vaccine. Fast injections are recommended when administering vaccines because of the potential for a reduction in pain, feasibility and practicality.

Trial registration: NCT02504398.

Keywords: Infant; Injection technique; Pain management; Speed of injection; Vaccination.