ABSTRACT
BACKGROUND: In the United States, children receive primary doses of M-M-RII (Merck & Co, Inc, West Point, PA) and Varivax (Merck & Co, Inc) beginning at 12 months, often at the same health care visit. Currently a second dose of M-M-RII is given to 4- to 6-year-old children, to increase vaccination rates and to reduce the number of individuals without detectable antibodies. A second dose of a varicella-containing vaccine may result in similar benefits. OBJECTIVES: To demonstrate that ProQuad (measles, mumps, rubella, and varicella virus vaccine live; Merck & Co, Inc) may be given in place of a second dose of M-M-RII or second doses of M-M-RII and Varivax for 4- to 6-year-old children. METHODS: Four- to 6-year-old children who had been immunized previously with M-M-RII and Varivax were assigned randomly to receive either ProQuad and placebo (N = 399), M-M-RII and placebo (N = 195), or M-M-RII and Varivax (N = 205) and were then monitored for safety and immunogenicity. RESULTS: ProQuad was generally well tolerated. Similarity (noninferiority) was demonstrated in postvaccination antibody responses to measles, mumps, and rubella between recipients of ProQuad and all recipients of M-M-RII and in responses to varicella between recipients of ProQuad and recipients of Varivax. Postvaccination seropositivity rates for antibodies against all 4 viruses were nearly 100% in all 3 groups. Small fold increases were observed for measles, mumps, and rubella antibody titers. In contrast, substantial boosts in varicella antibody titers were observed among recipients of a second dose of varicella vaccine, administered as ProQuad or Varivax. CONCLUSIONS: ProQuad may be used in place of a second dose of M-M-RII or second doses of M-M-RII and Varivax for 4- to 6-year-old children.
