The causes of low white blood cells in newborns include the following: First, it is caused by various viral infections. If a newborn has a viral infection, such as influenza virus or rhinovirus, respiratory syncytial virus, etc., these viral infections will cause a temporary drop in white blood cells, a symptom caused by the temporary suppression of hematopoietic function due to infection. As the infection is controlled in the newborn, the level of white blood cells will slowly rise. If the newborn has abnormal bone marrow hematopoiesis and is suffering from aplastic anemia, not only does the white blood cell count drop, but also the red blood cell and platelet counts are low, so the newborn should undergo a bone marrow aspiration to confirm the diagnosis.