Anaphylactic reaction following administration. Administer w/ caution to patients w/ thrombocytopaenia or a bleeding disorder. Syncope (fainting) can occur as a psychogenic response to needle inj. Antibody response in patients w/ endogenous or iatrogenic immunosuppression may be insufficient. Regarding passive protection, not all infants <6 mth born to women vaccinated during pregnancy will be protected. Interference w/ serological testing. Do not administer intravascularly.