Vaccination against measles, mumps, rubella and varicella (MMRV) is currently recommended in developed countries for infants from 12 months of age. However, measles vaccination at 9 months of age is recommended by the WHO in the Expanded Program on Immunization (EPI) schedule and it is therefore possible that MMR or MMRV vaccines might also be given at this age. This open-label, randomised, comparative study evaluated the immunogenicity and safety of a 2-dose schedule of ProQuad(®) (MMRV vaccine) given at a 3-month interval in healthy infants aged ≥9 months. For measles, the non-inferiority of the response rate post-Dose 2 was reached when Dose 1 was administered at 11 months (98%) compared with 12 months (99%) but was not reached when Dose 1 was administered at 9 months (95%). The response rate to measles post-Dose 1 increased with age, from 73% to 88% and 90% at 9, 11 and 12 months, respectively. For mumps, rubella and varicella, response rates were not different after Dose 1 (>95%) or Dose 2 (>99%) regardless of whether Dose 1 was administered at 9, 11 or 12 months of age. In conclusion, the age of administration of the first of a two-dose regimen of ProQuad may be lowered to 11 months. Dose 1 may be administered at 9 months if early protection is required, but it should be recognised that a second dose is required promptly with a minimum of 3-month interval between doses.

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