Need For Studies On People With Weakened Immune Systems: Vulnerability To Flu

Need For Studies On People With Weakened Immune Systems: Vulnerability To Flu And Response To Vaccination
22 Jul 2009

An article published in the August edition of The Lancet Infectious Diseases reports that additional research is required on the vulnerability to the new H1N1 flu strain of different immunosuppressed populations. The possible effectiveness and side-effects of future vaccines also need to be evaluated. The review is the work of Dr Ken M Kunisaki, Minneapolis VA Medical Center, USA, and University of Minnesota, USA, and Dr Edward N Janoff, Univeristy of Colorado Denver School of Medicine and Denver Veterans Affairs Medical Center, USA.

The study evaluated susceptibility in individuals with HIV/AIDS, cancer, people who received a solid organ transplant (SOT), or bone-marrow transplant (BMT), and patients on haemodialysis. The authors say: "Although influenza vaccination is widely recommended for people that are immunosuppressed, the same immune dysfunction that can increase the risk and consequences of influenza infection might also compromise vaccine responses and effectiveness."

Since the introduction of highly active antiretroviral therapy the numbers of HIV/AIDS patients admitted to hospital with flu have fallen considerably. But still, there are more admissions than for the general population. The US Centers for Disease Control and Prevention (CDC) recommends yearly flu vaccination. Vaccination appears safe, but it is not supported universally. In HIV/AIDS patients antibody responses to vaccination are generally lower. However, a number of studies suggest that vaccination leads to fewer and less severe cases of flu in HIV patients. There is a need for larger randomized trials to evaluate vaccination, mostly among those with low CD4+ cell counts.

Due to the immunosuppressant drugs they take to avoid organ rejection, people who received SOT generally have higher flu infection rates. Lung transplant recipients appear mostly at risk as the lungs are the primary site of flu infection. Kidney transplant recipients can suffer rejection if they contract flu.Theoretically, vaccination in these populations could also stimulate a T-cell response, leading to rejection. But the majority of studies suggest this does not happen. A crucial issue seems to be timing. The American Society of Transplantation recommends flu vaccination every year for all recipients of SOTs, beginning about 6 months after transplantation. Similar recommendations apply for recipients of bone marrow transplant (BMT). However, US guidelines recommend lifelong annual vaccination. On the other hand, European guidelines recommend individual evaluation of each case.

Chemotherapy can cause severe and intense immunosuppression for cancer patients. Between 21 to 33 percent of cancer patients have been estimated as being infected with flu when admitted to hospital with respiratory symptoms during a flu epidemic. Once more, timing of flu vaccination can be fundamental in cancer patients. The option might to vaccinate between chemotherapy cycles, or more than seven days before chemotherapy begins.

At the end of 2006, there were more than 327,000 people receiving haemodialysis treatment in the USA. Infections are the second leading cause of death in these patients. Lung infections (such as flu) kill higher proportions of dialysis patients than in the general population. An examination of US Medicare information indicated that vaccinated patients on dialysis had a significantly lower chance of hospital admission or death than unvaccinated patients.

In addition, the authors examined the use of corticosteroid. They mention that there is confirmation for patients taking these drugs that flu vaccination is both safe and often immunogenic. This applies for a patient taking these drugs either orally or by inhalation and either chronically or for a transitory period. However, the vaccine's clinical effectiveness in this population has not been adequately tested.

The authors call for further research into flu vaccination in all these particular populations. They also underline the value of other options to control flu infection, such as chemoprophylaxis using antiviral drugs. An observational study indicates that out of nineteen BMT patients with flu, none died. And 87 percent of them had taken oseltamivir (Tamiflu).

The authors write in conclusion: "We would particularly welcome randomised trials comparing standard influenza vaccine with active comparators such as modified vaccines or antiviral prophylaxis with or without vaccination. Such data would greatly enhance our ability to make more informed vaccination recommendations for this population, particularly in situations of vaccine shortage or pandemic influenza."

"Influenza in immunosuppressed populations: a review of infection frequency, morbidity, mortality, and vaccine responses"
Ken M Kunisaki, Edward N Janoff
Lancet Infect Dis 2009; 9: 493-504
The Lancet Infectious Diseases

Written by Stephanie Brunner (B.A.)
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