Evidence used to update the list of underlying medical conditions that increase a person’s risk of severe illness from COVID-19

The level of evidence for each condition was determined by CDC reviewers based on available information about COVID-19. Conditions were added to the list (if not already on the previous underlying medical conditions list [originally released in March 2020]) if evidence for an association with severe illness from COVID-19 met any of the following criteria:

  • Strongest and most consistent evidence: Defined as consistent evidence from multiple small studies or a strong association from a large study,
  • Mixed evidence: Defined as multiple studies that reached different conclusions about risk associated with a condition, or
  • Limited evidence: Defined as consistent evidence from a small number of studies.

Qualifiers to previously listed conditions were added or removed if there was strong evidence to support that the condition be expanded. Conditions previously listed were to be removed if there was strong and consistent evidence demonstrating no association with severe outcomes. Based on this criterion, no conditions were removed from the previous underlying medical conditions list dated March 2020; however, in this most recent update in November 2020, pregnancy was moved from “mixed evidence” to “strong evidence.”

*Updates to smoking were based on evidence available between December 1, 2019 and July 20, 2020.

Level of EvidenceConditionEvidence of Impact on COVID-19 Severity
Strongest and Most Consistent EvidenceCancerSystematic Review [6]Cohort Study [7,8]Case Series [9]
Chronic kidney diseaseCase Series [10, 1112]Cohort Studies [13, 14, 15]
COPDMeta Analyses [416]Case Series [17]Cohort Study [14]
Heart conditions, such as heart failure, coronary artery disease, or cardiomyopathiesCohort Study [1, 2]Meta Analyses [3, 4]Case Series [5]
Obesity (BMI> 30 kg/m2)Cohort Studies [18, 19, 20, 21, 22]Cross-sectional [23]
Severe Obesity (BMI ≥ 40 kg/m2)Cohort Study [98, 99]Cross-Sectional Study [95]Meta Analysis [107]
PregnancySystematic Review [54, 116]Case Control Study [55]Case Series [5657, 5859]Cohort Study [60, 61, 62, 117]
Sickle cell diseaseCase Series [24, 25, 26, 27, 28]
SmokingMeta Analyses [3, 16*, 63, 64, 65, 66, 101, 102, 104, 105]
Solid organ transplantationCase Series [12, 29, 30, 31, 32, 33, 34]Meta Analysis [100]
Type 2 diabetes mellitusCase Series [11]Longitudinal Study [35]Cohort Study [36, 37]Meta Analysis [38]Cross-Sectional Study [114]
Mixed EvidenceAsthmaCohort Study [14, 39, 40, 41]Case Series [17]
Cerebrovascular diseaseMeta Analysis [42, 43, 44, 45]Synthesis of Evidence [46]Cohort Study [1, 2, 474849]
HypertensionCohort Study [1, 2, 49, 50, 51, 91, 93]Case Series [92]Systematic Review [52]Meta Analyses [3, 4, 53, 94]
Use of corticosteroids or other immunosuppressive medicationsCase Series [67, 68, 69]Cohort Study [70, 71]
Limited EvidenceBone marrow transplantationReview [72]
HIVCase Series [73, 74]Cohort Study [109, 110, 111, 112]
Immune deficienciesCase Series [75]Systematic Review [76]
Inherited metabolic disordersCohort Study [47, 77]
Liver diseaseMeta-Analysis [78]Cohort  Study [79, 80, 118, 119]Literature Review [81]Case Control Study [120]
Neurologic conditionsCross-Sectional Study [82]Cohort Study [41, 49, 77]
Other chronic lung diseasesMeta-Analysis [4]Case Series [17]Cohort Study [14, 83]
Overweight (BMI > 25 kg/m2, but < 30 kg/m2)Cohort Study [96, 106]Case Series [97]Meta Analysis [115]
PediatricsSystematic Review [84, 85]Cross-Sectional Study [82, 86, 107]Cohort Study [77, 87, 88, 103, 108, 113,121, 122, 125]Case Series [123, 124]
ThalassemiaCase Series [89]Cross-Sectional Study [90]
Type 1 diabetes mellitusCase Series [11]Cohort Study [36, 37]Meta-Analysis [38]Cross-Sectional Study [114]

*Methodological issues found by other authors; re-analyzed by Guo [64] and an association finding risk factor for greater severity was found.

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