Lack of enrollment.

The purpose of this study is to assess the responses in the immune system of infants after they receive the vaccine against diphtheria, tetanus, and pertussis (DTaP). The investigators will do this by studying the immune cells and allergy responses in the blood prior to and after receipt of the third DTaP vaccine.

This is a single-site study of infants who are scheduled to receive their third series (~6 month) vaccinations, as routine care, to investigate whether the diphtheria, tetanus, and pertussis (DTaP) vaccination has an effect on specific immunoglobulin E (IgE) levels to milk, egg, or peanut. Infants will be assigned to one of two groups depending on the infant's sensitization to milk, egg, and peanut.

Inclusion Criteria:

• Written informed consent from parent/guardian

• General good health without other known need for blood draws that would conflict with the study volume requirements

• Aged 5 months - 7 months, any race/ethnicity, any gender

• Subjects must not have yet received their third DTaP vaccination, which typically is given at 6 months of age. Subjects must have previously received two doses of the DTaP vaccination, at ages 2 months and 4 months

• Willingness to return for follow-up testing as defined in the protocol and consent if screening tests indicate eligibility

• Group 1 participants must have all of the following:

  • A negative skin prick test to egg, milk, and peanut
  • A negative IgE to egg, milk, and peanut

• Group 2 participants must have all of the following:

  • A positive family history of allergic disease
  • Atopic Dermatitis not requiring prescription medication
  • A positive IgE to milk, egg, and/or peanut

If Group 1 enrollment is completed first, participants must have all of the following to be enrolled in Group 2:

• A family history of atopy
• Atopic dermatitis not requiring prescription medication

If Group 2 enrollment is completed first, participants must have all of the following to be enrolled in Group 1:

-No personal or family history of atopic disease

Exclusion Criteria:

• History of anemia requiring any treatment
• Previous allergic reaction to any food, defined as itching, rash, hives, swelling, vomiting, diarrhea, sneezing, rhinorrhea, wheezing, breathing difficulty, or passing out immediately after food ingestion.
• Evidence of non-IgE-mediated reaction to milk or soy (i.e. milk/soy protein intolerance) or evidence of food protein induced enterocolitis syndrome (FPIES)
• Severe atopic dermatitis (liberally defined as requiring prescription medication)
• Unable to obtain serum sample for determination of egg, milk and peanut IgE levels
• Use of short-acting anti-histamines (diphenhydramine, etc.) more than one time within 3 days of skin testing or on the day of skin testing
• Any history of intravenous or oral steroid medication
• Known underlying immune defect/deficiency or bleeding disorder

Infants who are scheduled to receive their ~6 month (third dose of primary series) vaccines including the DTaP vaccine as part of routine care.