Combination vaccines, which help provide protection against two or more diseases or against multiple serotypes of a single disease are increasingly used to help reduce the number of injections required for childhood immunization (1). Familiar combinations include measles, mumps, and rubella (MMR); diphtheria, tetanus, and whole-cell pertussis (DTP); poliomyelitis (serotypes 1-3); pneumococcal disease (23 serotypes); and influenza A and B. Recently a number of diptheria, tetanus, and acellular pertussis (DTaP) vaccines have received licensing approval, and DTaP is now recommended as the preferred combination in the United States, with DTP vaccine as an acceptable alternative (2). In the United States there have been only two recently licensed vaccines combining moieties that had previously required separate injections. A combination vaccine for Haemophilus influenzae type b (Hib) and hepatitis B (COMVAX®, Merck & Co., Inc., Whitehouse Station, NJ) is available for use beginning at 2 months of age and a combination DTaP/Hib vaccine (TriHIBit®, Pasteur Merieux Connaught, USA, Swiftwater, PA) is available for use at 15 months of age. Further combinations involving DTaP, Hib, inactivated poliomyelitis vaccine (IPV), and hepatitis B are licensed in Canada and European countries, and additional combinations, including MMR and varicella, are in clinical trials. Regulatory guidance on formulation, manufacturing, preclinical testing, and pre-licensure clinical trials of combination vaccines has recently been provided by the US Food and Drug Administration (FDA) (3).
