The cooperation between the American Academy of Family Physicians (AAFP), the American Academy of Pediatrics (AAP) and the Advisory Committee on Immunization Practices (ACIP) continues with the publication of a joint statement on combination vaccines for childhood immunization in this issue of American Family Physician¹; a complete copy with references is available from the AAFP by calling the order department at 800-944-0000 and asking for order no. 945. The statement also has been published in the May 7, 1999, issue of the recommendations and reports series of Morbidity and Mortality Weekly Report and in the May 1999 issue of Pediatrics.

The statement indicates that combination vaccines are an important way to reduce the discomfort from multiple injections and associated safety concerns.^2–5 Of note, vaccine combinations of diphtheria and tetanus toxoids and acellular pertussis and Haemophilus influenzae type b (TriHIBit) are currently not licensed for use in infants and should not be used in infants until they are licensed, because of concerns about interference with the Hib component.

Vaccines from different manufacturers to prevent the same disease may be interchanged when a particular antibody is known to protect against disease (called the serologic correlate of immunity) and when using vaccines from different manufacturers results in good antibody titers. Good titers occur when hepatitis B, hepatitis A and conjugate Hib vaccines from different manufacturers are used in a series. PRP-OMP Hib (PedvaxHIB) vaccine requires only two doses in the first year of life if it is the only Hib vaccine given (a third dose is recommended at 12 to 15 months of age). However, when both PRP-OMP and Hib vaccines from another manufacturer are given in the first year of life, then three doses are recommended for the infant series (the fourth dose is recommended at 12 to 15 months of age).

For diseases in which the serologic correlate of immunity is unknown, such as pertussis, it is preferable to use vaccines from the same manufacturer until data show good protection when vaccines from different manufacturers are used in series. Thus, when feasible, acellular pertussis vaccines from the same manufacturer should be used at least for the first three doses. If the manufacturer of a child's previous dose is unknown or that manufacturer's product is not available in the office, then any product may be used.

The document notes that clinicians should maintain a supply of vaccines to cover all of the diseases specified in the annual recommended childhood immunization schedule.⁶ Importantly, the document states that all brands need not be stocked.

Extra doses of an antigen are permitted when the benefits to the child outweigh the risk. Thus, an office that chose to stock the Hib-HepB combination vaccine instead of monovalent Hib could give the Hib-HepB combination for all doses of Hib. This is permissible even though some children receive a dose of hepatitis B vaccine at birth and thus would have received four doses of hepatitis B vaccine, one dose more than required. (Note: Hib and Hib-HepB combination should not be given earlier than six weeks of age because of decreased response and potential immune tolerance to Hib). Although normally recommended every 10 years, tetanus-diphtheria boosters may be given five years apart. However, the risk of side effects may be increased if extra doses of tetanus toxoid are given earlier than the recommended interval.

These principles should guide immunization practice and help clinicians stock needed vaccines without stocking multiple brands.