White blood cells of 2.2 x 10⁹/L are not severely low, they are moderately low. The normal value of white blood cells is (4~10) x 10⁹/L. 2.2 x 10⁹/L indicates that the white blood cells are below normal and are moderately low. The causes of low white blood cells include viral infections, drug-induced, and hematologic disorders. 1. Low white blood cells caused by viral infections are generally not serious, and will gradually return to normal after active antiviral treatment (e.g. oseltamivir). If the viral infection is serious and not taken seriously, it will lead to even lower white blood cells and increase the risk of secondary infections, jeopardizing health. 2. Certain drugs will have the complication of myelosuppression, leading to a decrease in white blood cells, such as malignant tumors after the use of chemotherapeutic drugs, myelosuppression occurs, the patient’s immunity decreases, the condition is more serious. 3. Blood system diseases, such as leukemia, aplastic anemia and other causes of leukopenia, not actively treated will have serious consequences, even life-threatening. Treatment of the cause is very important, such as acute myeloid leukemia to be a cytarabine and other drugs chemotherapy. When leukopenia occurs, it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment under the guidance of the physician.