The American board of Pediatricians states that: “Studies on the diversity of antigen receptors indicate that the immune system has the capacity to respond to extremely large numbers of antigens. Current data suggest that the theoretical capacity determined by diversity of antibody variable gene regions would allow for as many as 109 to 1011 different antibody specificities. But this prediction is limited by the number of circulating B cells and the likely redundancy of antibodies generated by an individual.”  And further on, the board explains that: “If vaccines overwhelmed or weakened the immune system, then one would expect lesser immune responses when vaccines are given at the same time as compared with when they are given at different times. However, the following vaccines induce similar humoral immune responses when given at the same or different times:  1) MMR and varicella  2) MMR, diphtheria-tetanus-pertussis (DTP), and OPV  3) hepatitis B, diphtheria-tetanus, and OPV  4) influenza and pneumococcus  5) MMR, DTP-Hib, and varicella  6) MMR and Hib and 7) DTP and Hib  Achieving similar immune responses by giving vaccines at the same time at different sites may be more easily accomplished than by combining vaccines in the same syringe. Challenges to giving many vaccines in a single injection are based partly on incompatibilities of agents used to buffer or stabilize individual vaccines. [1]  [1] Offit Paul, Addressing Parents’ Concerns: Do Multiple Vaccines Overwhelm or Weaken the Infant’s Immune System?, 01/01/2002,  , accessed 06/01/2011