This study compared the potency and immunomodulatory effects of measles mumps rubella (MMR) vaccine given to infants alone or in combination with varicella (MMR and V). In an additional group, NIMR vaccination was delayed 42 days to permit analysis of potential effects on underlying maturation of systemic immune functions. Assessment of immunity to the vaccines indicated consistent antibody production coupled with mixed Th1/Th2 memory, and no significant differences between vaccine groups or to the group who had their MMR vaccination delayed. Parallel analyses of cytokine responses to phytohaemagglutinin and tetanus toxoid did not detect any "bystander" effects of the vaccines on systemic immunity. (c) 2006 Elsevier Ltd. All rights reserved.