Longer needle length may boost efficacy of hepatitis B vaccine in obese adolescents

Longer, 1.5-inch needles yielded better results in obese adolescents after immunization with hepatitis B vaccine, when compared with standard needles, according to the results of a study published online today.

“Multiple hypotheses have been offered for disparity in vaccine immune response on the basis of BMI, including the possibility that standard needle length recommendations do not account for the increased length needed to penetrate the deltoid fat pad and into the muscle of obese adolescents and adults,” Amy B. Middleman, MD, an Infectious Diseases in Children editorial board member, and other researchers noted in the study.

From December 2001 to October 2004, researchers enrolled 24 patients, aged 14 to 24 years, at city clinics, a health fair and a high school in Houston. The researchers randomly assigned one group of 14 patients to the 1.5-inch needle group and the remaining 10 patients to the 1-inch needle group.

The researchers noted that the 1.5-inch needles produced significantly higher hepatitis B surface antigen (median=345.3 mIU/mL) in the patients when compared with the group that received the 1-inch needles (median=189.8 mIU/mL).

“This supports the hypothesis that inadequate muscle penetration is responsible, at least in part, for lower immune response to [hepatitis B] vaccine among obese adolescent and adult vaccine recipients,” Middleman and colleagues wrote. “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.” – by Melissa Foster

Middleman AB. Pediatrics. 2010;125:e000.

Size does matter. This small study of 14 adolescents suggests that obese adolescents may need a 1.5 inch needle for their vaccinations in order to optimize intramuscular injection and subsequently improve antibody responses — an important consideration for the occasional marginal sero-responder.

Similarly in a 2007 Pediatric Infectious Disease article we further examined the effects of BMI and immunogenicity after three doses of quadrivalent human papillomavirus vaccine in nearly 500 preteen and young teenage girls. We likewise observed a comparable problem most likely due to insufficient needle length in larger girls.

Our investigators used a 1 or 2 inch needle to vaccinate in the deltoid muscle. Comparing girls whose BMI was ≥ 28 with those <28, the antibody concentrations (GMT) for HPV serotypes 16 and 18 were nearly half in the overweight girls (2,531 vs 5,195 and 538 vs 1,065, respectively). We did not think that obesity inherently caused the lower GMTs.

A formal large sample study comparing GMTs with needle length and BMI needs to be performed with the adolescent vaccines. Otherwise our vaccine program may be no more than a shot in the dark for our overweight patients and for girls who intrinsically have higher BMIs than boys.

– Stan L. Block, MD
Infectious Diseases in Children Editorial Board

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