Pain from intramuscular vaccine injection in adults

background: vaccine use has been increasing worldwide, and adult populations are presented with more opportunities to experience pain from vaccine injection. the insertion of a needle through the skin is the most common source of iatrogenic pain, and needle phobia is a major concern in medical practice. however, it is unclear which factors play major roles in the perception of pain from vaccine injection in adults. aim: to evaluate the influences of patient characteristics on pain perception due to intramuscular vaccine injection in healthy adult volunteers. material and methods: the injection of hepatitis b vaccine using a 24 mm, 24-g needle was performed as a uniform stimulus, and the intensity of injection pain was measured immediately after the injection using a 100-mm visual analogue scale (vas). the influences of patient characteristics on pain intensity were investigated. results: one hundred sixty volunteers (65 males, 95 females) were enrolled in this study. the average vas score was 20.8 ± 17.1 (range 0 to 67) in males and 34.4 ± 19.7 (range 2 to 76) in females (p < 0.001). however, there were no correlations between vas score and age, body mass index or maximal pain score from previous painful experiences. the vas score was also not affected by the experience of previous vaccine injections, a history of childbirth in females, or religion. conclusions: gender appears to be the only major factor that influences the pain of intramuscular vaccine injection. therefore, pain-reducing methods will be needed when performing injection procedures, particularly in women.