Fatalities from mononucleosis are extremely rare in developed nations. However, chronic sub-clinical infection may persist secondary to the dormant virus within the B cells. Reactivation of the virus may occur in susceptible hosts under the appropriate environmental stressors. Similar such reactivation or chronic sub-clinical viral activity in susceptible hosts may trigger multiple host autoimmune diseases and cancers secondary to virus predilection to B lymphocytes and its ability to alter both lymphocyte proliferation and lymphocyte antibody production.
Uncommon, non-fatal complications exist, including various forms of CNS and hematological affection.