Seroconversion Rates and Measles Antibody Titers Induced by Measles Vaccination in Latin American Children Six to 12 Months of Age

Abstract

A collaborative study was conducted to determine how 2,042 infants responded serologically to measles vaccination in six study areas and to help define the optimal age for measles vaccination in children of Latin America. The results suggest that local factors affect the seroconversion rate and that a success rate of 90% can be attained if initial vaccination is given at nine to 11 months of age, depending on the area. Post-vaccination titers also varied, and higher titers were generally observed in groups with higher seroconversion rates.A collaborative study was conducted in 6 areas of Latin America to determine the serologic response to measles immunization of 2042 infants. The most significant finding was that antibody titers after vaccination were lower for younger than for older infants. The average vaccination age at which an 80% seroconversion rate was achieved was 8.5 months while a 90% seroconversion rate was not achieved on average until 10 months. Similarly, the geometric mean titer was 29 for the average 6-month-old infant compared with 83 among 12-month-old-infants. Higher titers were generally observed in infants with higher seroconversion rates. Infants whose weights were 60-85% of the norm for their age seemed to have better seroconversion rates than those closer to the weight-for-age norm. Urban-rural differences in seroconversion rates were not observed. In general, the seroconversion rates in Latin America are intermediate between those in Africa and North America. These results suggest that local factors affect the seroconversion rate and a success rate of 90% can be attained in Latin America if initial vaccination is given at 9-11 months of age. If measles vaccine is administered too early, more failures can be expected and lower levels of maternal antibodies will be passed on to the next generation.