Shingles is a painful, blistering skin rash that can last for months or even years. It's caused by the varicella-zoster virus, the same virus that causes chickenpox. It's thought to strike more than a million people over the age of 60 each year in the U.S.
Every year, health officials urge individuals 50 and older to get vaccinated against the virus. The vaccine boosts cell-mediated immunity to the virus and can decrease the incidence and severity of the condition.
But in a two-year study, Irwin, the first author of the research and director of the UCLA Cousins Center for Psychoneuroimmunology, and his colleagues measured immune responses to the shingles vaccination among 40 people aged 60 or older who suffered from a major depressive disorder and compared these responses to similar levels in 52 control patients matched by age and gender. Measurements were taken at the beginning of the study, and then at six weeks, one year and two years after the patients received either the shingles vaccine or a placebo.
Depressed patients not being treated with antidepressants showed a weaker immune response to the varicella-zoster virus and thus were less able to respond to the shingles vaccine than patients who were not depressed and patients who suffered from depression but were receiving treatment with antidepressants.
The findings suggest that patients with untreated depression were "poorly protected by the shingles vaccination," Irwin said.
Surprisingly, when the depression was being treated, responses to the vaccine were normalized, even when the depression treatment had not been effective in lessening the symptoms of depression.
"Among depressed elderly, treatment with an antidepressant medication such as a selective serotonin uptake inhibitor might increase the protective effects of zoster vaccine," said Irwin.
Larger studies are needed to evaluate the possible relationship between untreated depression and the risk of shingles, the study noted, along with further research to establish what mechanisms are responsible for patients' reduced immune response.
And there is a clinical side as well, Irwin noted. "Efforts are also needed to identify and diagnose depressed elderly patients who might benefit from either a more potent vaccine or a multi-dose vaccination schedule." he said.
The findings have important public health implications beyond the prevention of shingles, possibly extending to other infectious diseases, Irwin said. Because this study measured immune system T cells that were specific to the varicella-zoster virus, the association may extend to T cells specific for antigens of other pathogens that cause disease in older adults, such as influenza.
If so, Irwin said, this suggests that untreated depression may identify a sub-group of elderly likely to respond poorly to other vaccines.
"While we know that psychological stress is associated with a weakened immune response to influenza vaccines in older adults, few studies have examined the association between depression and infectious disease risk, or disease-relevant immunologic endpoints, such as vaccine responses," he said.