One combined measles-mumps-rubella (MMR) vaccine without Human Serum Albumin (HSA) is currently licensed in the USA (M-M-R II; Merck, USA) and another has been developed (Priorix™ [MMR-RIT, GSK, Belgium]). In this follow-up study, children from USA or Puerto Rico, who had received one dose of M-M-R II or MMR-RIT at 12-15 months of age in the primary study (NCT00861744), were followed-up for 2 y post-vaccination. Anti-measles and anti-rubella antibodies were measured using Enzyme-Linked Immunosorbent Assay (ELISA), and anti-mumps antibodies using ELISA and plaque reduction neutralization (PRN) assays. Serious adverse events (SAEs) were recorded during the entire follow-up. The according-to-protocol (ATP) persistence cohort included 752 children (M-M-R II = 186, MMR-RIT = 566), who received primary vaccination at a mean age of 12.3 ( ± 0.67) months. 104 children were revaccinated with MMR-containing vaccines; therefore, serology results for timepoints after revaccination were excluded from the analysis. Seropositivity for measles (Year 1≥ 98.3%; Year 2≥ 99.4%) and rubella (Year 1≥ 98.9%; Year 2 = 100%) remained as high at Year 2 as at Day 42. Similarly, seropositivity for mumps determined by ELISA (Year 1≥ 90.1%; Year 2≥ 94.1%) and PRN assays (Year 1≥ 87.5%; Year 2≥ 91.7%) persisted. Thirty-three SAEs were recorded in 23 children; 2 SAEs (inguinal adenitis and idiopathic thrombocytopenic purpura) and one SAE (febrile convulsion) were considered as potentially related to MMR-RIT and M-M-R II, respectively. This study showed that antibodies against measles, mumps and rubella persisted for up to 2 y post-vaccination with either MMR vaccine in children aged 12-15 months, and that both vaccines were well-tolerated during the follow-up period.
Keywords: MMR vaccine; Priorix; antibody persistence; measles; mumps; rubella.