Can Depression Stifle Response to a Common Vaccine?
A paper was recently published that investigates how patients suffering from major depression may respond to a specific vaccine. The authors studied the connection between this mental health disorder and the immune response to the varicella zoster virus vaccine. The varicella virus is more commonly known as virus that causes the chickenpox. It is an interesting virus because following infection; it remains inactive in the infected individual’s sensory neurons. In other words, if you are infected with this virus it essentially hangs around in your body and can re-infect you at a later time. If this re-infection does proceed via reactivation and replication, then it can lead to Herpes zoster (HZ), otherwise known as shingles. Shingles is a fairly well known syndrome that is characterized by a painful skin rash with blisters. Each year, there are more than a million new cases of shingles each year. The main risk factor for developing this type of viral infection is age. The incidence and severity of shingles increases with age.
As of yet, the main other identified risk factor is a low level of VZV-specific T cell-mediated immunity. VZV-specific T cell-mediated immunity is basically a measurement of how ready your immune system is to responding to varicella reactivation. A “higher” level of this immunity means your body is more capable of fighting off the dreaded shingles infection. Post-varicella infection, your body is able to develop and maintain this immunity. So although the virus that causes shingles may be hanging around in your neurons, waiting to attack, your body’s natural defenses are often ready to fight back.
But in some cases, this immune response isn’t strong enough. In fact, some individuals are at greater risk because their bodies are less able to prevent the varicella virus from re-infecting and causing shingles. The authors of this recently published study recognized that both age and immunity are significant risk factors for shingles. They also noticed that other studies had observed lower levels of immunity in older adults with major depression as compared to non-depressed individuals. This information caught their attention. Could individuals with depression be less able to fight off the infection that causes shingles? In order to further investigate this connection, the authors measured the level of immunity against shingles in subjects with depression that were untreated and those that were treated with anti-depressants. They measured the immunity by taking blood samples from older individual patients and determining how many immune cells they possessed that could be capable of essentially recognizing the invading varicella virus. This procedure was done for blood from patients without depression, patients with treated depression, and patients with untreated depression. In a broad sense, the study aimed to answer the question: Does depression affect immunity against shingles? The answer to this question has important implications for the efficacy of the vaccine that is used to prevent shingles. If depression does affect immunity against shingles, then the vaccine to prevent shingles would likely affect depressed and non-depressed patients in different ways.
The authors of this study delved into their work with these questions in mind. After many tests, their results reveal a very interesting connection between depression and susceptibility to the Herpes zoster virus that causes shingles. In general, administration of the zoster vaccine boosts or patient immunity, thereby decreasing the incidence and severity of shingles in older individuals. Overall, however, the vaccine did not boost immunity in elderly individuals with untreated depression. In contrast, the vaccine boosted immunity in elderly individuals with depression who were being treated with antidepressants. This increase in immunity upon vaccination was comparable to the increase in immunity upon vaccination that was observed in non-depressed subjects. Overall, the baseline immunity against shingles and the immunity post-vaccination were substantially lower in elderly subjects with untreated depression!
This study presents a puzzling connection, and a connection that has important public health implications. The incidence and severity of the Herpes zoster virus is increased in individuals with decreased immunity. Elderly individuals with untreated depression are not only at risk for developing shingles because of their age, but this study now suggests that they are also at risk due to their untreated depression. These individuals are therefore at greater risk of developing shingles and associated complications. One of the more potentially extreme complications is postherpetic neuralgia, which is characterized by severe nerve damage following shingles infection. This symptom can cause severe pain for months or even years following infection! Adults over the age of 50 are encouraged to receive the Herpes zoster vaccine as a part of routine medical care. Given the recent findings, however, a simple vaccine may not be sufficient to protect older adults with untreated depression.
While more research is needed to better understand the connection between depression and decreased efficacy of vaccine-induced shingles immunity, these findings should begin to be applied to the clinical setting. Elderly individuals with untreated depression should be prioritized for preventative treatments aimed at protecting them from developing shingles and potential health complications associated with shingles. Specific steps should be taken so that this group of elderly individuals is not even more susceptible to shingles. For instances, these patients may benefit from administration of more potent or multi-dose vaccines that can induced sufficient immunity to fight off reactivation of the virus that causes shingles. They may also be encouraged to seek antidepressant treatment prior to vaccination in order to increase the vaccine’s efficacy.
In order to address these public health concerns, more research within this field is needed. The present study highlights a very interesting connection between depression and anti-viral immunity to a specific viral infection. These results may, however, have implications for the risk of other infectious diseases. As the authors note, depression is associated with a decreased number memory T cells that are specific to varicella virus infection (and therefore a decreased immunity against the virus). These cells are responsible for recognizing and mounting an immune response against foreign invaders. If depression is associated with a decrease in varicella virus-specific memory T cells, then it is possible that this disorder is also associated with a decrease in memory T cells that are specific to other viruses responsible for other infectious diseases, such as influenza. In this case, individuals with untreated depression may be more vulnerable to developing potentially dangerous infections. Such increased susceptibility must be addressed via public health regulations. These cohorts of potentially more vulnerable patients may need to be identified and treated with stricter anti-viral treatments. The next time an elderly patient with depression comes in for a routine vaccination, assisting medical professional may need to think twice about how best to alter a vaccination to ensure that it protects that individual from dangerous viral infections. This study is a reminder to clinicians and patients that vaccines, like treatments, should be tailored to each individual patient!
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