*1.2.1 Spectrum of severity and case fatality rates*

The spectrum of symptomatic infection ranges from mild to critical; most infections are not severe. Specifically, disease severity may be classified as:


Since many severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections are asymptomatic, the infection fatality rate (ie, the estimated mortality rate among all individuals with infection) is considerably lower and has been estimated by some analyses to be between 0.5 and 1 percent. Conversely, the reported case fatality rates are likely underestimates of the true case fatality rates, as many fatal infections are undiagnosed. Neither the case fatality rate nor the infection fatality rate account for the full burden of the pandemic, which includes excess mortality from other conditions because of delayed care, overburdened health care systems, and social determinants of health.

## *1.2.2 Risk factors for severe illness*

Severe illness can occur in otherwise healthy individuals of any age, but it predominantly occurs in adults with advanced age or certain underlying medical comorbidities. Specific demographic features and laboratory abnormalities have also been associated with severe disease.

#### *1.2.3 Increasing age*

Individuals of any age can acquire SARS-CoV-2 infection, although adults of middle age and older are most commonly affected, and older adults are more likely to have severe disease.

In several cohorts of hospitalized patients with confirmed COVID-19, the median age ranged from 49 to 56 years.

Older age is also associated with increased mortality. In contrast, individuals aged 18 to 34 years accounted for only 5 percent of adults hospitalized for COVID-19 in a large health care database study and had a mortality rate of 2.7 percent; morbid obesity, hypertension, and male sex were associated with mortality in that age group.

Symptomatic infection in children and adolescents appears to be relatively uncommon; when it occurs, it is usually mild, although a small proportion experience severe and even fatal disease.
