Consistent with clinical study data on the timing of fever and measles-like rash, an analysis of a post-marketing observational safety study in children (N=31,298, 99% in their second year of life) receiving their first dose of vaccine has shown that febrile seizures occurred more frequently 5-12 days following vaccination with ProQuad (n=22; 0.7 per 1000 children) when compared with data from children in a historical, age- and gender- matched, control group vaccinated with the measles, mumps, and rubella vaccine manufactured by Merck & Co., Inc., and the Varicella Vaccine live (Oka/ Merck) concomitantly (N=31,298) before ProQuad was available (n=10; 0.3 per 1000 children).