Several studies have noted that obese adolescents and adults achieve lower titers of antibody in response to vaccines such as hepatitis B virus (HBV) vaccine. The objective of this study was to determine whether use of a longer (1.5-in) rather than a standard (1-in) needle to penetrate the thicker deltoid fat pad among obese youth would result in higher antibody titers after immunization against HBV.


Obese adolescents from a large metropolitan area who had not previously received the HBV vaccine were randomly assigned to be immunized with HBV vaccine by using either a 1-inch or a 1.5-inch needle.


Those who were immunized with a 1.5-inch needle achieved significantly higher antibody titers to hepatitis B surface antigen (median titers: 1-inch = 189.8 mIU/mL, 1.5-inch = 345.4 mIU/mL; P = .03).


This finding supports the hypothesis that needle length accounts for a significant portion of the discrepancy in immune response to HBV vaccine that is seen among those with obesity.

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