Titer of live attenuated viral vaccines, such as measles-mumps-rubella (MMR) vaccinations, vary across batches and during a batch’s shelf life, with the maximum titer predicted upon batch release. 

In phase III, randomized, controlled research, researchers evaluated the safety profile of an upper-range release titer MMR-RIT lot to commercial MMR II lots since higher titers may potentially lead to greater reactogenicity. At 12 to15 months of age, they vaccinated 1736 children with MMR-RIT (N = 1164) or MMR II (N = 572), both provided as first doses with varicella, hepatitis A, and pneumococcal conjugate vaccines at 12-15 months of age. 


The incidence of fever 5 to 12 days after MMR-RIT and MMR II immunization was comparable: 4.2% vs 3.1% for fever > 39.0°C and 18.2% vs 17.1% (difference: 1.1%) for fever ≥ 38.0°C, which matched the primary goal. Within 43 days after receiving MMR-RIT, two occurrences of febrile convulsions were documented. Rashes were recorded in 24.4% and 27.4% of children on Days 0 to 42, respectively, with measles/rubella-like rashes in 5.8% and 4.7%. Measles-like infections were observed in 1.5% and 0.9% of children 5 to 12 days after immunization, respectively. Immune thrombocytopenic purpura after MMR II immunization was deemed a vaccine-related adverse event. Immune responses in both groups were comparable. In summary, the safety profile of an upper-range release titer MMR-RIT lot was comparable to that of commercial MMR II lots, with both vaccines reporting similar rates of fever and other MMR-specific symptoms and low rates of measles-like diseases.