This correspondence is to document the circumstances regarding this infant's recent adverse reaction to the Haemophilus influenzae type B (Hib) vaccination. The infant has been followed up by a doctor since the 1st year of life for anaphylaxis to cow's milk. Skin test reactivity was noted to peanut and egg protein at the time of initial evaluation and thus, these foods have been avoided. By current AAP Redbook recommendations, precautions with MMR are not necessary but at the pediatrician's request special precaution with MMR was undertaken. The infant received this vaccination as 0.1 ml into the right thigh followed by 0.4 ml into the left thigh with two localized urticarial lesions noted on the left thigh in the area the MMR was administered. He was treated uneventfully with Benadryl at that time, and the urticaria resolved within 10 minutes. Other vaccinations including DTaP and Varivax were administered on 10/09/99, again, uneventfully. The infant has received the Haemophilus influenzae type B (Hib) previously without adverse reaction. On 03/30/00, Haemophilus influenzae type B (Hib) was administered as ProHIBit, the Haemophilus influenzae type B - diphtheria toxoid conjugate vaccine. He was observed for 20 minutes in your office and was discharged home after a seeming uneventful vaccination. The infant began to develop urticaria within 15 minutes followed by cough and rhinorrhea. He was treated with Benadryl and the doctors office was called. The infant was reported to have increased cough and worsening symptoms and, thus, the infant's mother was advised to administer Epi-Pen Jr and call 911. Upon arrival in the ER, the infant was noted to have significant urticaria, but no angioedema or signs of respiratory distress. The upper airway was clear and the chest was clear to auscultation. The infant was treated with Prednisone, Zantac, another dose of Benadryl, and another dose of epinephrine. The treating physician in the ER regarded the infant's anaphylactic reaction as "mild" and the infant was observed until the event resolved. A review of the package insert for ProHIBit reveals that this is a Haemophilus influenzae type B polysaccharide covalently bound to diphtheria toxoid protein with thimerosal added as a preservative. It is unclear which component of the vaccine is responsible for the anaphylactic reaction, but thimerosal has been implicated in other adverse reactions to vaccines. The physician's recommendations are: 1- Avoid thimerosal containing vaccines and eyedrops. Further assessment of thimerosal allergy will be undertaken if they can obtain some thimerosal for this purpose. 2-No further vaccination with ProHIBit should be offered. The infant will be due for repeat Haemophilus influenzae type B vaccination at five. A HIB titer may be obtained at that age to assess his immunity and if the titer is protective, repeat vaccination can be avoided. 3-The infant should receive diphtheria and tetanus boosters DT) at appropriate ages. However, precautions should be undertaken with these vaccinations and should best be administered in the allergist's office. 4-Caution administration of all future vaccinations is advised. Theses may best be administered in the office of an allergist and administered in an incremental fashion. The infant should be observed for one hour after each future vaccination.