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Measles vaccination of infants in a well-vaccinated population
M M Carson1, D W Spady, P Albrecht
1Department of Pediatrics, University of Alberta, Edmonton, Canada.
Insights
Early measles vaccination before 15 months is effective in infants, even with maternal immunity. This study evaluated serologic responses to measles immunization in infants younger than the recommended age.
Area of Science:
- Pediatrics
- Immunology
- Vaccinology
Background:
- Measles outbreaks necessitate vaccination for at-risk infants 6 months and older.
- Maternal immunization status influences infant immune response to vaccination.
- Assessing early measles immunization efficacy is crucial given evolving demographics.
Purpose of the Study:
- To evaluate the serologic response to early measles immunization in infants.
- To compare immune responses based on maternal immunization history.
- To determine the effectiveness of measles vaccination before the standard age.
Main Methods:
- Prospective trial involving 125 infants receiving monovalent measles vaccine (6-8.5 months) and measles-mumps-rubella (MMR) vaccine (15 months).
- Serologic response measured by plaque reduction neutralization (PRN) assay and enzyme immunoassay.
- Infants categorized into three groups based on maternal immunization history.
Main Results:
- Pre-vaccination antibody titers were significantly higher in infants with natural maternal immunity (Group 1) compared to other groups.
- Seroconversion rates for monovalent measles vaccine varied: 31% (Group 1), 71% (Group 2), and 76% (Group 3).
- Post-MMR vaccination, over 97% of infants achieved protective antibody titers (>120) and were measles IgG-positive.
Conclusions:
- Measles vaccination before the currently recommended age is effective, particularly in infants from well-vaccinated maternal populations.
- Early immunization can elicit a protective immune response, even in the presence of maternal antibodies.
- The study supports considering earlier measles vaccination strategies for infants.
Abstract:
During outbreaks of measles, measles vaccine is recommended for infants considered to be at risk who are 6 months of age and older. In a prospective trial the serologic response to early measles immunization has been evaluated in 125 infants given monovalent measles vaccine at 6 to 8.5 months of age and measles-mumps-rubella at 15 months. The response to vaccination was measured by plaque reduction neutralization (PRN) assay and enzyme immunoassay. Infants were grouped by the mother's immunization history: natural immunity (n = 60, Group 1); killed followed by live, further attenuated vaccine (n = 22, Group 2); and live, further attenuated vaccine only (n = 43, Group 3). The prevaccination geometric mean titer (GMT) by PRN for Group 1 (GMT = 69) was significantly higher than that of Group 2 (GMT = 18) or 3 (GMT = 13). Seroconversion (4-fold increase in PRN titer) rates after monovalent vaccine were 31, 71 and 76% for Groups 1, 2 and 3, respectively. Seroconversion percentages were higher when measured 6 to 8 weeks after vaccination compared with 4 to 5 weeks. After measles-mumps-rubella > or = 97% of all infants had PRN titers > 120 and were measles IgG-positive by enzyme immunoassay. These data show that as demographics shift to a well-vaccinated maternal population and susceptibility in younger infants, measles vaccination before the currently recommended age will be effective.