From MedscapeCME Clinical Briefs
Laurie Barclay, MD
February 12, 2010 — Use of a longer needle results in significantly higher titers in response to hepatitis B virus (HBV) vaccine among obese adolescents, according to the results of a randomized study reported online in the February 8 issue of Pediatrics.
"Obese youth achieve lower titers than average-weight peers in response to hepatitis B vaccine when a 1-inch needle is used," write Amy B. Middleman, MD, MSEd, MPH, from Baylor College of Medicine in Houston, Texas, and colleagues.
The goal of the study was to evaluate whether using a longer (1.5-inch) vs a standard (1-inch) needle to penetrate the thicker deltoid fat pad among obese youth who had not previously received the HBV vaccine would achieve higher antibody titers after immunization against HBV. The investigators randomly assigned 65 obese adolescents from a large metropolitan area to be immunized with HBV vaccine using either a 1-inch or a 1.5-inch needle. Analyzable data were available for 10 adolescents in the 1-inch needle group and for 14 in the 1.5-inch needle group.
Compared with obese adolescents immunized with a 1-inch needle, those who were immunized with a 1.5-inch needle had significantly higher antibody titers to hepatitis B surface antigen (median titers 189.8 mIU/mL with the 1-inch needle; 345.4 mIU/mL with the 1.5-inch needle; 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," the study authors write.
Limitations of this study include sample size smaller than planned with loss of participants to follow-up, few male participants, limited ability to enroll patients who had not yet received HBV vaccine, and limited variability in race and ethnicity (most participants were Hispanic).
"As we continue to experience high rates of obesity in the United States and throughout the world, additional evidence-based research on optimizing the effective delivery of immunizations to adolescents and young adults will be critical," the study authors conclude. "Following updated needle length recommendations will be a first step toward improving the health of our youth and young adults by preventing vaccine-preventable diseases."
Pediatrics. Published online February 8, 2010.
Previous evidence suggests that obese adolescents and adults tend to have lower antibody titers than their nonobese peers when immunized with HBV or other vaccines. Given the increasing number of vaccines targeting adolescents, and the rising rates of obesity in this population, this observation may be of some concern.
The reasons underlying the disparity in vaccine immune response based on body mass index are still unknown. One possibility is that use of the standard needle length does not penetrate the deltoid fat pad and into the muscle of obese adolescents and adults. The less abundant blood supply in adipose tissue may delay vaccine antigen presentation to the B and T cells involved in immune response.