He had a minor illness and was able to leave the hospital quickly.
Patients with mild symptoms were allowed to recuperate at home.
軽傷 (けいしょう) refers to a minor physical injury, whereas 軽症 (けいしょう) with different kanji refers to a mild illness or light symptoms of disease.
person with mild symptoms; mild case
Compound of 軽 (light, mild) and 症 (symptom, illness).