Needle Length and Injection Technique for Efficient Intramuscular Vaccine Delivery in Infants and Children Evaluated Through an Ultrasonographic Determination of Subcutaneous and Muscle Layer Thickness

The relationship between resulting reactogenicity and immunogenicity with route and site of vaccine injection is well documented.1-5 Preference for intramuscular injection is given for aluminum-adsorbed vaccines (eg, diphtheria, tetanus, pertussis, and inactivated poliovirus [DTP-IPV], hepatitis A, and hepatitis B vaccines), because superficial administration leads to increased incidence of local reactions.6 A better immune response for intramuscular compared with subcutaneous injection has been seen with several vaccines, such as the hepatitis B,1,5 rabies,3 and influenza2vaccines. Both the injection technique and the needle length are crucial for ensuring proper intramuscular delivery and thus are directly related to vaccine safety and immuno-genicity. Guidelines concerning the choice of the injection technique and needle length have been presented. Two injection techniques are currently recommended. The first, widely used in the United States, requires bunching the thigh muscle at the injection site to increase muscle mass and to minimize the chance of striking bone.6 The second, recommended by the World Health Organization (WHO), suggests stretching the skin flat between the finger and thumb, and pushing the needle down at a 90° angle through the skin.7 With respect to needle length, both the WHO and the Committee on Infectious Diseases of the American Academy of Pediatrics support the use of 7/8-inch (22-mm) or longer needles for intramuscular delivery.7,8 Some unidose vaccines are supplied in disposable syringes, equipped with 5/8-inch (16-mm) sealed needles that have been designed to provide an efficient, precise, and user-friendly tool for intramuscular injection. Nevertheless, the adequacy of this shorter needle (compared with the 7/8-inch needle) has been questioned.6 To determine the optimum needle size for intramuscular injection and eventually to make a correlation between needle length and appropriate injection technique, one must have …