SAN FRANCISCO—As the nation prepares for influenza season, the susceptibility of immunosuppressed individuals, including transplant recipients, to the new H1N1 influenza strain (“swine flu”) and efficacy of the new H1N1 vaccines in these populations remain unclear.

Nevertheless, a medical epidemiologist believes transplant recipients and other immunosuppressed individuals receive the new vaccines.

“I think if I were a renal transplant patient, I would get vaccinated before influenza strikes in my community,” said Gaston De Serres, MD, PhD, of Laval University in Quebec, Canada. “If I have flu-like symptoms during the time influenza is circulating in my community, I should go and consult early [with my physician], not late.”

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At the 49th annual meeting here of the Interscience Conference on Antimicrobial Agents and Chemotherapy, Dr. De Serres spoke about the H1N1 vaccines approved by the FDA on September 15.

Over the next six months, more will be known about how safe and effective the H1N1 vaccines are in immunocompromised patients, he said. Based on preliminary data from adults participating in multiple clinical studies, the H1N1 vaccines induce a robust immune response in most healthy adults eight to 10 days after a single dose, as occurs with the seasonal influenza vaccine.

Ongoing clinical studies will provide additional information about the optimal dose in children. The recommendations for dosing will be updated if indicated by findings from those studies. As with the seasonal influenza vaccines, the 2009 H1N1 vaccines are being produced in formulations that contain thimerosal, a mercury-containing preservative, and in non-thimerosal formulations. Patients with severe or life-threatening allergies to chicken eggs, or to any other substance in the vaccine, should not be vaccinated.

Patients who receive solid organ transplants (SOT) generally have higher influenza infection rates because of the immunosuppressant drugs they take to prevent organ rejection, Dr. De Serres noted. Lung transplant recipients seem particularly at risk as the lungs are the primary site of flu infection.

Kidney transplant recipients can suffer organ rejection if they contract influenza. In theory, vaccination in these populations could also stimulate a T-cell response, leading to rejection. However, most studies suggest this does not occur.

Flu can cause organ rejection

“Seasonal influenza has been reported to cause rejection of the transplanted kidney, so preventing influenza in kidney transplant recipients is important,” said Ken Kunisaki, MD, Assistant Professor of Medicine at the University of Minnesota in Minneapolis.

“While kidney transplant recipients may not have as good antibody responses to influenza vaccine as people without transplants, a substantial proportion still responds. Therefore, kidney transplant recipients should receive influenza vaccination, in accordance with guidelines from the American Society of Transplantation. Unfortunately, there are not enough data about swine flu in transplant recipients and its vaccine to make firm conclusions and recommendations at this time.”

With seasonal influenza, a key issue appears to be timing. The American Society of Transplantation recommends flu vaccination every year for all recipients of SOTs, beginning six months after transplantation. U.S. guidelines recommend lifelong annual vaccinations; European guidelines recommend individual patient assessment.

Estimates show that more than 327,000 people were receiving hemodialysis treatment in the United States at the end of 2006. Infections are the second leading cause of death in these patients, and lung infections such as influenza claim a higher proportion of lives among dialysis patients than the general population.

An analysis of Medicare claims data showed that flu-vaccinated patients on dialysis had a substantially lower chance of hospitalization or death from any cause than unvaccinated patients.

Chemotherapy can produce acute and profound immunosuppression in cancer patients and studies suggest that 21%-33% of cancer patients may be infected with influenza when admitted to a hospital with respiratory symptoms during a flu epidemic. Again, timing of flu vaccination may be crucial in cancer patients.  The response to flu vaccination might be best between chemotherapy cycles or more than 7 days before chemotherapy starts.

“Patients receiving chemotherapy for cancer appear to be at heightened risk for influenza-related complications,” Dr. Kunisaki said.

“They also appear less likely to respond to influenza vaccine, but nevertheless, a fair proportion still responds. No formal guidelines exist for influenza vaccination of patients receiving chemotherapy, but the data suggest timing vaccination to either more than two weeks before receiving chemotherapy or between chemotherapy cycles.”