This article is from the Childhood Vaccinations FAQ, by Lynn Gazis-Sax firstname.lastname@example.org with numerous contributions by others.
People with HIV, nephrosis, severe asthma, and similar chronic
diseases, but especially leukemia. Conditions for vaccination of
leukemic children are: remission for at least a year, off maintenance
therapy for a week before and a week after getting the vaccine, and
cellular immunity intact. (Catalana)