We are concerned that the external validity of the findings by Reis et al,1 who evaluated measures to reduce the acute pain of multiple immunizations in infants, may be limited by their use of inappropriately short needles.
Nearly all inactivated vaccines recommended during infancy in the United States are licensed only for intramuscular injection. An exception, inactivated poliovirus vaccine, may be given intramuscularly or subcutaneously. To ensure intramuscular penetration when immunizing infants approximately 2 months old, the American Academy of Pediatrics, Elk Grove Village, Ill2; the American Academy of Family Physicians, Leawood, Kan; and the federal Advisory Committee on Immunization Practices, Atlanta, Ga,3 recommend a needle length of 2.22 to 2.54 cm (⅞-1 in). In contrast, Reis and colleagues immunized infants of this age with needles 1.59 cm (⅝ in) in length. The bore of the needles used in their study was 26 gauge, narrower than the recommended range of 22 to 25 gauge.2,3
Hammer SJ, Backer H, Schechter R. Immunization Injections. Arch Pediatr Adolesc Med. 2004;158(7):708. doi:10.1001/archpedi.158.7.708-b