NEW YORK (Reuters Health) – The results of a new study indicate that the intradermal vaccination route offers greater protection against influenza than the standard intramuscular route in elderly adults.

As reported in The Journal of Infectious Diseases for September 1, Dr. David Holland, from Middlemore Hospital in Auckland, New Zealand, and colleagues compared the immunogenicity of intradermally and intramuscularly administered influenza vaccines in 1107 volunteers over 60 years of age.

The intradermal trivalent inactivated influenza vaccine was given using a new microinjection system designed to provide consistent vaccination as well as ease and convenience. The prefilled syringe has a beveled microneedle that protrudes 1.5 mm from the syringe and has a penetration depth limiter.

Compared with the control vaccine, the intradermal vaccine was associated with significantly higher strain-specific hemaglutination inhibition geometric mean titers at post-vaccine day 21. Seroprotection rates, seroconversion rates, and average titer increases were also generally higher with the intradermal vaccine.

With the exception of pain, erythema and other local injection site reactions were more common with the intradermal vaccine than with the intramuscular vaccine.

“We have shown, for what we believe to be the first time, that the intradermal vaccination route can be used to provide immunogenicity that is significantly superior to that achieved using conventional intramuscular vaccination,” Dr. Holland’s team concludes.

In a related editorial, Dr. Janet E. McElhaney, from the University of Connecticut in Farmington, and Dr. Jan P. Dutz, from the University of British Columbia in Vancouver, Canada, comment that “the investigators are to be commended for recruiting ‘healthy’ older adults, including those with chronic diseases common in this population. This type of recruitment will help to ensure that the results will be replicated in the general population of older persons.”

J Infect Dis 2008;198:632-634,650-658.