A low number of WBCs is called leukopenia. It may be due to:Bone marrow failure (for example, due to infection, tumor),collagen-vascular diseases,disease of the liver or spleen,radiation.Other causes are:uremia,steroid treatment,aplastic anemia.AIDS (Acquired Immune Deficiency Syndrome),multiple sclerosis,myasthenia gravis, and Guillain-Barre syndrome are the other causes which can cause low white blood cell count.Certain medications can also cause low WBC count.
If your WBC count is low,the first thing is to find out the cause & its treatment is according to cause.Remember low WBC count is not a disease but a symptom of an underlying disease. So the underlying disease is to be diagnosed.For this you have to consult Hematologist who will perform certain tests & scans.
You are more prone to get the infections including swine flu.You are more prone to get the viral infections first & then if the WBC count is too low then you can also get the bacterial infections.So I conclude that you are more prone/vulnerable to both viral & bacterial infections.