by Theo Schall


I was recently asked to find out how many Americans are immunocompromised. To my surprise, I discovered that this isn’t a number that anyone tracks. Because immune deficiencies (by definition) put patients at risk, this is a potentially dangerous oversight.


People with weakened immune systems are especially vulnerable to infection. They may have problems with infections that recur, persist longer than usual, or are atypically severe. Minor infections like the common cold can be life-threatening. Recurrent infections can put patients who become “frequent fliers” at hospitals at greater risk of further contracting hospital-acquired infections.


As a result of this vulnerability, the immunocompromised bear a higher burden during disasters. Planning for public health measures and emergency preparedness requires consideration of the needs of immunocompromised people to reduce that disproportionate burden. Usually this kind of planning would start with a look at the incidence and prevalence of a public health issue, yet these measures don’t seem to exist for immunocompromised patients as a group.


The diversity of causes of immunodeficiency may be the main reason that no one tracks the total number of affected patients. In a 2002 paper, researchers estimated that around 10 million people were immunocompromised, but they counted only “recipients of organ transplants, individuals with diagnosed and undiagnosed HIV infection or AIDS, and patients with cancer.”


Patients can either be born with an immune deficiency or they can acquire one. While it’s relatively rare to be born with an immune deficiency, over 200 different hereditary and genetic defects can cause a “primary” immunodeficiency. Acquired immune deficiency also has a variety of causes, including cancer and its treatments, the immunosuppressant drugs taken by transplant recipients and people with autoimmune disorders, malnutrition, aging, and HIV/AIDS. The estimate of 10 million mentioned above excludes a number of these groups.


Another reason that no one tracks the total number may be the politics of disease: there are advocacy groups for immunodeficiency, but they only speak for patients with primary forms of the disorder, not acquired immunodeficiency. Given that these advocacy groups represent patients with rare disorders who have few treatment options, their position is understandable. Unfortunately, it has the effect of fracturing a larger group of people who face similar challenges.


So who should we be counting?
This list is not exhaustive, but is an attempt to illustrate the challenges of a comprehensive tally. Note that the categories below are not mutually exclusive; individuals might, for example, be older and malnourished (which is actually a common occurrence).


People living with HIV and AIDS

  • More than 1.2 million Americans have HIV/AIDS. Around 14% of them don’t know they have HIV, which may make them especially vulnerable to other opportunistic infections.

Older adults

The malnourished

People with cancer, especially those undergoing treatment

  • The American Cancer Society estimates the number of new cancer cases each year. For 2015, that number is 1,658,370.
  • As of January 2014, the estimated number of survivors of the 10 most common cancers was 14 million.
  • The number of cancer patients whose immune systems are currently suppressed by treatment protocols is somewhere in between these figures. Many patients who were diagnosed last year are still in treatment, whereas plenty of the long-term survivors have likely finished their treatment processes.

Transplant recipients

  • According to the American Transplant Association, over 617,000 transplants have occurred in the U.S. since 1988. However, this is not the number of currently living recipients, which is likely to be significantly lower. Life expectancy for transplant recipients has improved in the past couple of decades, but it is still lower than that of the general population.

Other patients on immunosuppressant drugs

  • Some patients with severe autoimmune disorders like lupus benefit from immunosuppressive drugs.
  • The number of Americans with autoimmune disorders is estimated to be between 20 and 50 million, however, the number currently taking immunosuppressive drugs is likely to be a small percentage of the total.

People with primary immunodeficiency

  • In 2005, the number of people living with a diagnosed primary immunodeficiency disease was estimated at 250,000.


I wish I could leave you with a range of estimates, but there are too many unknowns: how many patients belong to more than one group? How many transplant recipients are living? How many patients with autoimmune disorders take immunosuppressants? And what other groups are immunosuppressed? Individually, these are challenging questions. In aggregate, this line of inquiry has broad implications for our how we design health systems to protect the most vulnerable patients.

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Theo Schall

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