This article is from the Childhood Vaccinations FAQ, by Lynn Gazis-Sax email@example.com with numerous contributions by others.
The vaccine should not be administered to persons with a history of
hypersensitivity reactions to any of the vaccine components, including
alum or the preservative (2-phenoxyethanol). Because it is
inactivated, no special precautions need be taken when vaccinating
immunocompromised individuals. The inactivation also means that they
theoretical risk to a fetus is low, but there are no data to determine
the safety of the vaccine during pregnancy. People mildly ill at the
time of vaccination may get the vaccine, but people moderately to
severely ill should wait until they recover.