The prevalence of immunosuppression from health conditions and medication use among US adults is often reported to be about 3%, which is based on an estimate of 2.7% from nationally representative data1 from 2013 and an estimate of 2.8% for the prevalence of immunosuppressive drug use2 among commercially insured adults younger than 65 years of age.
Immunosuppression prevalence is an important consideration for public health in the US given this population’s increased risk from viral and bacterial infections. These estimates were of particular concern during the COVID-19 pandemic because people with immunosuppression are less likely to have an adequate response to vaccines and are more likely to experience severe COVID-19 symptoms even after vaccination.3 This population has also been advised to continue with COVID-19 precautions to avoid infection.4
In addition, immunocompromised conditions and medication use may have changed over the last decade. We present population prevalence estimates of immunosuppression among US adults using nationally representative data from 2021.
We estimated the prevalence of immunosuppression among US adults aged 18 years or older by sex, age, race and ethnicity, and health insurance status using the 2021 National Health Interview Survey (NHIS). Race and ethnicity were assessed to examine how immunosuppression has changed for demographic groups examined in previous studies. Rates of chronic illness are variable by race and ethnicity. The NHIS is a nationally representative annual health survey conducted in person and partially by telephone.5 It was redesigned in 2019 with different sampling frames.
The 2021 household response rate was 52.8%. Extensive procedures are used to adjust for sample design and nonresponse. The University of Washington considers the NHIS to not involve human subjects (as defined by federal regulations and guidance) and does not require institutional review board approval or review.
In 2021, the NHIS asked the full adult sample questions about immunosuppression for the first time since 2013. We used 5 of the same questions (Box) as used in the analysis1 of the 2013 NHIS data to determine the current sample of participants with immunosuppression. However, in the current analysis individuals who reported immunosuppressive health conditions, medication use, or treatments within the past 12 months were considered to have immunosuppression (the duration of medication use was 6 months in the analysis1 of the 2013 NHIS).
Box Section Ref IDBox.
2021 National Health Interview Survey Questions on Immunosuppressiona
Do you currently have a health condition that a doctor or other health professional told you weakens the immune system?
During the past 12 months, have you taken prescription medication or had any medical treatments that a doctor or other health professional told you would weaken your immune system?
Have you ever been told by a doctor or other health professional that you had cancer or a malignancy of any kind?
What kind of cancer was it?
How old were you when a doctor or other health professional first told you that you had cancer?
a The data on immunosuppression in the Table are based on responses from 29 359 participants to these survey questions. Immunosuppression was present if the participant responded “yes” to question 1 or question 2 or if the participant reported having hematologic cancer within the past 2 years (based on question 4 and date calculations from question 5). Those not meeting this definition were categorized as not having immunosuppression.
The analysis used NHIS-recommended weighting procedures, including the use of designated survey design variables to adjust for sample design and nonresponse. Weighted proportions and 95% CIs were calculated using the svy procedures in Stata SE version 17 (StataCorp) to estimate the national generalizable prevalence.5
Of the 29 164 (unweighted) eligible adults, 6.6% (95% CI, 6.2%-6.9%) (weighted) had current immunosuppression based on their reported health conditions, prescriptions, and medical treatments. The weighted prevalence was 4.4% for having an immunosuppressive condition, 3.9% for taking an immunosuppressive medication, and 1.8% for both; the weighted prevalence of having hematological cancer was 0.1%. These categories were not mutually exclusive.
The prevalence for women was 7.9% (95% CI, 7.4%-8.4%) and for men was 5.2% (95% CI, 4.8%-5.7%) (Table). The rates were highest for American Indian or Alaska Native respondents (8.4%; 95% CI, 6.0%-11.7%), White respondents (7.4%; 95% CI, 6.9%-7.8%), for those aged 60 to 69 years (9.5%; 95% CI, 8.6%-10.5%), and for those with insurance (6.9%; 95% CI, 6.6%-7.3%).
In this study using the 2021 NHIS, an estimated 6.6% of US adults had immunosuppression. This rate of immunosuppression was higher than the previous national estimate of 2.7% using the 2013 NHIS,1 yet the patterns in the distribution of immunosuppression by sex, race, and age were similar.1
The increase in self-reported immunosuppression over an 8-year period may be due to increased use of immunosuppressive medications. For example, the number of filled Medicaid prescriptions for adalimumab (used to treat various autoimmune conditions) increased 3.5-fold between 2014 and 2021.6 Increases in immunosuppressive conditions or increased awareness about one’s immunosuppressed status in light of the COVID-19 pandemic also could contribute to these increases.
Study limitations include reliance on self-reported immunosuppression and the lack of data on the specific causes of immunosuppression. In addition, the immune-suppressing medication time frame was 6 months in the 2013 NHIS instead of the 1-year time frame in the present study.
Given the documented increase in immunosuppression, studies are needed to understand the causes for this increase.