Young, healthy individuals given a low dose of influenza vaccine by injection under the skin rather than into a muscle develop a vigorous antibody response, researchers report.

In light of this year’s flu shot shortage, dose-sparing strategies that could stretch out the available supply should be considered, Dr. Gregory M. Glenn and colleagues at Iomai Corporation in Gaithersburg, Maryland, point out in the New England Journal of Medicine.

Their article was released early by the Journal, and is due to be published November 25th.

Up until now, the intra-muscular injection route has been used for flu vaccines because of “tradition and convenience,” Glenn told AMN Health. However, skin is actually a “very attractive target for immunization” because of its high concentration of immune cells that pick up and present “foreign” antigens to the rest of the immune system.

In June of this year, Glenn’s group randomly assigned 100 subjects between 18 and 40 years old to get an intra-muscular injection of a normal dose of flu vaccine or an intra-dermal injection of one-fifth the normal dose.

After 21 days, there were no significant differences between the two groups in their antibody responses to two of the three strains of the flu bug in the vaccine, while the response to the third strain was actually stronger with the intra-dermal injection.

There were more local reactions associated with the intra-dermal method, but these were “trivial,” Glenn noted, and just reflect the greater immune response that can be achieved with this type of inoculation.

Whether public health authorities will recommend a dose-sparing strategy for this year remains to be seen, he said. But even if it is not used this year, he suspects that further studies will be completed by next year’s flu season, when the flu vaccine supply may still be limited.

SOURCE: New England Journal of Medicine, November 25, 2004.