The antibody persistence rates 1 year postvaccination in recipients of a single dose of ProQuad were 98.9% (1722/ 1741) for measles, 96.7% (1676/ 1733) for mumps, 99.6% (1796/ 1804) for rubella, and 97.5% (1512/ 1550) for varicella (≥ 5 gpELISA Units/ ml).