Age issues cast doubt on intradermal flu shots

More promising for future than this season

Kenney RT, Frech SA, Muenz LR, et al. Dose sparing with intradermal injection of influenza vaccine. N Engl J Med 2004; 351.

Belshe RB, Newman FK, Cannon J, et al. Serum antibody responses after intradermal vaccination against influenza. N Engl J Med 2004; 351.

La Montagne JR, Fauci AS. Intradermal influenza vaccination — Can less be more? N Engl J Med 2004; 351.

These two studies and an accompanying editorial caused quite a stir recently in light of the influenza vaccine shortage.

The studies indicate flu vaccine supplies could be expanded by administering doses into the skin rather than into muscle. They raise the possibility of maximizing scarce vaccine because smaller doses can be used to prompt an immune reaction in skin cells.

In particular, the study by Kenney, et al. found that in young adults "intradermal administration of one-fifth the standard intramuscular dose of an influenza vaccine elicited immunogenicity that was similar to or better than that elicited by intramuscular injection."

That means some health care workers and contacts of high-risk groups may benefit, but the critical question concerns the elderly.

In that regard, Belshe, et al. concluded, "The intradermal route seemed better suited for younger subjects. . . . Less vigorous responses were observed in older persons in both the intradermal and intramuscular groups, and the response to the A/Panama strain (H3N2) in the intradermal group was significantly lower than that in the intramuscular group."

While emphasizing that the studies hold much promise for pandemics and boosting immunity, the editorial sounded a note of caution:

"In addition to the basic research and clinical challenges that the current studies bring to mind, there are technical challenges that must be addressed, including the special training of personnel who would be needed to administer vaccinations through the intradermal route effectively," the editorial stated.

"There is also the issue of regulatory challenges that must be addressed to allow, under special circumstances, a degree of flexibility in the administration of vaccine by a route that was not originally used in the critical path toward licensure of a given product," it concluded.

SARS transmission requires close contact

Environmental contamination also a factor

Leung GM, Hedley AJ, Ho LM, et al. The epidemiology of severe acute respiratory syndrome in the 2003 Hong Kong epidemic: An analysis of all 1,755 patients. Ann Intern Med 2004; 141:662-673.

New research suggests that severe acute respiratory syndrome (SARS) has relatively low transmissibility except in settings of close contact or with clinically significant environmental contamination.

An epidemiological analysis of all 1,755 cases from Hong Kong found that most cases clustered in hospitals and residential buildings. Close human contact and spread by a sewage system probably explain the clustering, the authors reported.

The outbreak lasted about three months. The estimated mean incubation period was 4.6 days, and the case-fatality ratio was 17%. Factors associated with increased risk for death included older age and male sex. There were 302 deaths among the 1,755 cases. Overall, 49.3% of patients were infected in clinics, hospitals, or elderly or nursing homes, and the Amoy Gardens residential cluster accounted for 18.8% of cases. Health care workers accounted for 23.1% of all reported cases.