A. It’s not necessarily a risk factor for infection, but a small number of studies appear to show that individuals with BMI > 30 (defined as “obese”) and BMI > 40 (defined as “severely obese”) are more likely to be hospitalized than individuals with BMI <30 (which includes individuals of “normal” weight and “overweight”).
Other studies show that individuals who are obese are more likely to need ventilation or are more likely to be admitted to acute and critical care units than individuals who are non-obese. These patterns are especially pronounced among adults < 60 or < 65 years of age (depending on the study) but not among older adults.
Excess body fat can induce immune dysregulation and chronic inflammation which is linked to the cytokine storm responsible for Acute Respiratory Distress Syndrome in respiratory diseases like COVID-19. Abdominal obesity, especially, can cause compression of the diaphragm and lungs. So there is a biological mechanism for this pattern.
What we don’t know so far:
Is obesity the only risk factor for worse progression or do these individuals have other underlying conditions which contribute to more complications? Some studies have accounted for other underlying conditions but not all.
Are individuals who are obese less likely to seek care earlier on (or only when it’s too late), and might delays in care-seeking behavior (or limited access to care) contribute to more severe presentation of disease at admission?
Would these findings hold up in an analysis of the general population which includes mild, asymptomatic individuals? The studies, to date, have included subjects that have interacted with the healthcare system. We do not know if obese individuals have worse progression of COVID than non-obese individuals in the general population.
See here for a summary of the studies so far.