More research is needed on the susceptibility of a range of immunosuppressed populations to the new H1N1 flu strain, as well as the possible efficacy and side-effects of forthcoming vaccines. The issues are discussed in a Review in the August edition of the Lancet Infectious Diseases, written by 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 authors look at susceptibility in people with HIV/AIDS, cancer, those who have had a solid organ transplant (SOT), or bone-marrow transplant (BMT), and patients on haemodialysis. They 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."
Numbers of HIV/AIDS patients admitted to hospital with flu have fallen substantially since the advent of highly active antiretroviral therapy. But admissions are still higher than the general population. The US Centers for Disease Control and Prevention (CDC) recommends yearly flu vaccination, although support for this is not universal, despite vaccination appearing safe. Antibody responses to vaccination are generally lower in HIV/AIDS patients; but several studies have shown that vaccination leads to fewer and less severe cases of flu in HIV patients. Larger randomised trials are needed to assess vaccination, particularly among those with low CD4+ cell counts.
People who received SOT generally have higher flu infection rates due to the immunosuppressant drugs they take to prevent organ rejection. Lung transplant recipients seem particularly at risk as the lungs are the primary site of flu infection. Kidney transplant recipients can suffer rejection if they contract flu. In theory, vaccination in these populations could also stimulate a T-cell response, leading to rejection—but most studies suggest this does not occur. A key issue appears to be timing, with the American Society of Transplantation recommending flu vaccination every year for all recipients of SOTs, beginning about 6 months after transplantation. Similar recommendations apply for recipients of BMTs; however, US guidelines recommend lifelong annual vaccination whilst European guidelines recommend individual assessment of each case.
For cancer patients, chemotherapy can produce acute and profound immunosuppression, and 21-33% of cancer patients have been estimated as being infected with flu when admitted to hospital with respiratory symptoms during a flu epidemic. Again, timing of flu vaccination can be crucial in cancer patients. The response might be best between chemotherapy cycles, or more than 7 days before chemotherapy starts.
More than 327,000 people were receiving haemodialysis treatment in the USA at the end of 2006. Infections are the second leading cause of death in these patients, and lung infections such as flu kill higher proportions of dialysis patients than people in the general population. An analysis of US Medicare claims data showed that vaccinated patients on dialysis had a substantially lower chance of any-cause hospital admission or any-cause death than unvaccinated patients.
The authors also looked at corticosteroid use, saying that the evidence suggests that for patients taking these drugs—either oral or inhaled, and either chronically or for a transient period—flu vaccination is both safe and often immunogenic. However, the vaccine's clinical effectiveness in this population has not been well tested.
As well as calling for more research into flu vaccination in all these populations, the authors stress the importance of other options to control flu infection, such as chemoprophylaxis using antiviral drugs. An observational study showed that none out of 19 BMT patients with flu died, when 87% of them had taken oseltamivir (Tamiflu).
The authors conclude: "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."
Dr Ken Kunisaki, Minneapolis VA Medical Center, USA T) +1 612 467-4400 E) kunis001@umn.edu
For full Review, see: http://press.thelancet.com/tlidimsupp.pdf
For Comment on possible origin of swine flu see: http://press.thelancet.com/tlidflurr.pdf
linked editorial: http://press.thelancet.com/tlidfluedit.pdf
Journal
The Lancet Infectious Diseases