July 1, 2009

Patients With Kidney Transplants May Benefit Less From Flu Shots

A new report shows that kidney transplant patients have a weaker response to flu vaccines than healthy individuals, especially in the first six months after receiving a transplant.

Kelly A. Birdwell of Vanderbilt University Medical Center noted that transplant patients are known to be at an increased risk for respiratory viral infections, which can be particularly harmful to people with suppressed immune systems.

The Centers for Disease Control and Prevention urges kidney transplant patients to get influenza vaccinations, but little is known about what kind of antibody response they are able to mount to a flu shot.

The study, to be published in July in the American Journal of Kidney Diseases, examined the response to influenza vaccine in 53 kidney transplant recipients and 106 healthy controls during the 2006-2007 flu season"”all received tacrolimus for immunosuppression.

So far, no exclusive research has been done for patients on tacrolimus, which is now the most commonly used immunosuppressant in kidney transplant patients.

In order to determine the vaccine response, the researchers tested the participants' levels of antibodies to three different influenza strains"”A/H1N1, A/H3N2, and B"”before they received the vaccine and again one month later.

The effectiveness of the vaccine was measured by the patients' seroresponse, which is a four-fold increase in levels of antibodies against a viral strain, and seroprotection, which are the levels of antibodies adequate for protection against infection.

Seroresponse or seroprotection was achieved in a smaller percentage of the transplant patients than in the healthy controls. However, only the A/H3N2 strain showed statistically significant differences.

Patients who had undergone transplants within the last six months were considerably less likely than the healthy controls to show seroresponse or seroprotection to any of the three viral strains contained in the flu shot.

However, patients are typically on the highest doses of immunosuppressant medication to prevent their bodies from attacking the transplanted organ during the first six months after transplant"”meaning they have a weaker immune system, and a weaker response to the flu vaccine, Birdwell said.

But there are several possible approaches to providing additional protection against the flu to kidney transplant patients.

"Possibilities include the provision of a booster dose of the influenza vaccine, or the use of an adjuvant, or substance given along with a medication or vaccine to enhance its effects," Birdwell said.

She also suggested the live intranasal vaccine may provide a more vigorous protective response.

Additionally, Birdwell noted it should be taken into consideration that any new influenza vaccines"”including those targeting H1N1, also known as the swine flu"”may not provoke the same protective response in kidney transplant patients.

Dr. Kerry Willis, Senior Vice President for Scientific Activities, National Kidney Foundation, said kidney transplant recipients should still follow the CDC recommendation to be immunized against influenza.

"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," he said.


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