NEW YORK (Reuters Health) - Kidney transplant recipients receiving immunosuppression treatment with tacrolimus may have a diminished response to influenza vaccination, especially within 6 months of transplantation, researchers report in the July issue of the American Journal of Kidney Diseases.

"Despite our findings, our results indicate that the majority of kidney transplant recipients do mount a protective response to the influenza vaccine. Thus, the public health benefits of the vaccine support its continued use in this population," Dr. Kelly A. Birdwell of Vanderbilt University Medical Center in Nashville, Tennessee, told Reuters Health.

In a prospective study conducted during the 2006-2007 influenza season, Birdwell and colleagues compared the influenza vaccine-induced antibody response in 53 kidney transplant recipients administered tacrolimus-based regimens with the response in 106 healthy control subjects.

"For the 2006-2007 inactivated influenza vaccine, a lower proportion of kidney transplant recipients on tacrolimus-based immunosuppression regimens responded to the vaccine than did the healthy controls, although this was significant only for the A/H3N2 influenza strain," Birdwell reported.

For the A/H3N2 strain, 62.3 percent of controls had a response, defined as a 4-fold increase in antibody titer 1 month after vaccination, compared with only 34.0 percent of the transplant patients. In addition, 91.5 percent of controls achieved protection levels, compared with only 69.8 percent of transplant patients.

In particular, patients transplanted within the last 6 months were significantly less likely than controls to achieve a response or protection to any of the three viral strains contained in the influenza vaccine, the researchers found.

"Further studies," Birdwell concludes, "are needed to understand the complex nature of vaccine response in these patients, so as to provide improved protection for all patients in the future."

In the meantime, "kidney transplant recipients should still be immunized against influenza, as recommended by the CDC," Dr. Kerry Willis, Senior Vice President for Scientific Activities at the National Kidney Foundation, noted in a statement.

"There are several promising approaches to providing additional protection against the flu for these patients, but more research is necessary before any can be recommended," Willis added.

SOURCE: American Journal of Kidney Diseases, July 2009.