The diagnosis might also be considered if there is a family history where relatives were affected by illnesses found in X-linked lymphoproliferative syndrome (XLP), such as fatal Epstein-Barr virus (EBV) infection, lymphoma or hypogammaglobulinemia.    From Wordnik.com.  [X-linked Lymphoproliferative Syndrome] Reference

Those in whom immunity fails to develop, those too young to be vaccinated, those who have immune deficits like hypogammaglobulinemia, and those who are immunosuppressed from chemotherapy or HIV are all at risk from unvaccinated children in their schools and neighborhoods.    From Wordnik.com.  [this won't hurt a bit] Reference