Immunogenicity and safety of a booster dose of live attenuated measles-mumps-rubella vaccine for 4-year-old children
Objective 
To evaluate the immunogenicity and safety of a booster dose of live attenuated measles-mumps-rubella (MMR) vaccine for 4-year-old children and to provide references for reasonable arrangement of MMR immunization schedule. 
 
 
Methods 
Children aged 4 years (54-60 months) old were recruited and divided into three groups as follows: Group 8 months MR [receiving live attenuated measles and rubella (MR) vaccination at 8 months and MMR vaccination at 18 months], Group 8 months MMR (receiving MMR vaccination at both 8 and 18 months) and Group 12 months MMR (receiving MMR vaccination at both 12 and 22 months). Active follow-up was conducted for safety evaluation after immunization of all subjects with the booster dose of MMR vaccine. Blood samples were collected before and 35 days after vaccination and analyzed by ELISA to detect serum antibodies to measles, mumps and rubella. 
 
 
Results 
A total of 514 subjects were enrolled in this study of safety evaluation and 469 of them received serologic detection of antibodies twice. The rate of adverse reactions following vaccination was 17.12% (general reactions accounted for 94.21%) and no severe adverse reactions were reported. No significant difference in the rates of adverse reactions was found among the three groups (χ2=4.82, P=0.090). Subjects who were seropositive for measles, mumps and rubella increased after immunization with MMR vaccine, accounting for 100%, 99.79% and 99.79%, respectively. Geometric mean concentrations (GMC) against measles, mumps and rubella in all subjects were 1.35, 3.05 and 2.13 times higher than what they were before the immunization. Levels of antibodies to measles, mumps and rubella were all increased significantly in the three groups after immunization with the booster dose of MMR vaccine (Fisher Exact Test, P=0.000). 
 
 
Conclusion 
The booster dose of MMR vaccine increases the levels of serum antibodies in children aged 4 years old with high safety. It suggests that two doses of MMR vaccine should be encouraged in the immunization program in China. 
 
 
Key words: 
MMR vaccine; Immunogenicity; Safety