Kidney transplant patients have a weaker response to influenza immunization than healthy individuals, especially in the first six months after receiving a transplant, according to a study published in the July issue of the American Journal of Kidney Diseases, the official journal of the National Kidney Foundation.
Respiratory viral infections are common among transplant patients, and are cause for concern because they can be particularly harmful to people with suppressed immune systems, noted Kelly A. Birdwell, MD, MSCI, of Vanderbilt University Medical Center in Nashville, Tennessee in her report.
Should transplant recipients receive a flu shot?
The Centers for Disease Control and Prevention recommends influenza vaccine for kidney transplant patients, but little is known about what kind of antibody response they are able to mount to a flu shot. What's more, no studies have looked exclusively at patients on tacrolimus, now the most commonly used immunosuppressant in kidney transplant patients.
The researchers looked at the response to influenza vaccine in 53 kidney transplant recipients and 106 healthy controls during the 2006-2007 flu season. All of the patients were receiving tacrolimus for immunosuppression.
Dr. Birdwell and her team checked vaccine response by testing study 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 researchers used two criteria to gauge the effectiveness of the vaccine: seroresponse, defined as a four-fold increase in levels of antibodies against a viral strain; and seroprotection, meaning levels of antibodies adequate for protection against infection.
A smaller percentage of the transplant patients achieved seroresponse or seroprotection than the healthy controls. But the differences were statistically significant only for one strain, A/H3N2; among controls, 62.3% achieved seroresponse, compared to 34% of the transplant patients, while 91.5% of controls and 69.8% of transplant patients were seroprotected.
Patients who had undergone transplants within the last six months were significantly less likely than the healthy controls to show seroresponse or seroprotection to any of the three viral strains contained in the flu shot. Dr. Birdwell and her team point out that during the first six months after transplant, patients are typically on the highest doses of immunosuppressant medication to prevent their bodies from attacking the transplanted organ. This translates to a weaker immune system, and a weaker response to the flu vaccine.
There are several possible approaches to providing additional protection against the flu to kidney transplant patients, Dr. Birdwell said. "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," the researcher said.
"In addition, the live intranasal vaccine may provide a more vigorous protective response, though the use of a live vaccine in this immunosuppressed population certainly requires formal investigation for safety and efficacy. As always, routine hand washing is one of the best defenses."
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, she added, and this should be taken into consideration.
"Kidney transplant recipients should still be immunized against influenza, as recommended by the CDC," said Dr. Kerry Willis, Senior Vice President for Scientific Acitivies, National Kidney Foundation. "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."