Measles antibody in mothers and infants 0-2 years and response to measles vaccine at the age of 9 and 18 months.

BACKGROUND: Despite the declining trends in measles cases corresponding to an increase in routine measles immunization coverage, measles outbreaks occur in some isolated areas in Nan province, northern Thailand. The primary reason for these outbreaks is inadequate vaccine coverage. Another reason is primary vaccine failure. OBJECTIVES: To study maternal and cord blood measles antibody, the kenetic change of infant measles antibody from 0-9 months and the response to measles vaccine at the age of 9 and 18 months. MATERIAL AND METHOD: A prospective cohort study for measles antibody of 1,010 mothers and infants 0-2 years was done between April 1999 and March 2001 at three hospitals in Nan province. Consecutive blood samples were drawn for measles antibody measurement by ELISA assays at Virus Research Institute, National Institute of Health, Thailand. The demographic data of mothers and infants were recorded at each visit. RESULTS: Maternal and cord blood measles antibody were high and the authors found a higher level in cord blood than in maternal level. Measles antibody level in infants declined significantly from the age of 4 months (246.4 +/- 364.2 mlU/L) to their lowest level at the age of 9 months (17.7 +/- 197.1 mlU/L). CONCLUSION: After the first dose of 9-month measles vaccination, the authors found the seroconversion rate of 82.2 percent. The seroconversion rate was significantly higher to 99.6 percent after the second dose at 18 months old.

Antibody response after measles immunization.

RATIONALE: Measles is still an important public health problem in Thailand despite measles vaccination being practiced since 1984. Vaccine failure is one of the suspected reasons for the high incidence of measles. OBJECTIVE: To study the seroconversion rate of 9-month-old infants and to study the antibody level in 18 month-old and 4 year-old children who had measles vaccination at 9 months of age. MATERIAL AND METHOD: Enrolled infants and children who attended the child health clinic for routine immunization at the Queen Sirikit National Institute of Child Health from March 1, 1994 to May 31, 1995. They were divided into 3 groups. Group A, 9 month-old infants who came for measles vaccination. Blood samples were drawn twice from these infants, before measles vaccination and 3 months later for measles antibody level. Group B and C were 18 month-old and 4-year-old children who came for their first and second DTP (Diphtheria, Tetanus, Pertussis vaccine) booster. One blood sample for measles antibody was drawn from the latter group of children. Measles antibody was determined by micro-neutralization technic at the National Institute of Health (NIH). The geometric mean antibody titer before and after measles vaccination was compared by using the paired t-test. RESULTS: There were 30, 31 and 34 infants/children in group A, B and C respectively. No significant measles antibody (NT antibody was less than 1:4) was detected in 93.5 per cent of 9-month-old infants. The seroconversion rate at 3 months after vaccination in group A children was 68.75 per cent while in group B, 9 months after vaccination it was 53.3 per cent. Ninety seven per cent of children in group C had NT antibody above 1:4. The geometric mean titer (GMT) of measles antibody in 9-month (before vaccination), 12-month, 18-month infants and 4 year old children was 1:2.5; 1:14.8, 1:8.2 and 1:73.8, respectively (p < 0.05). CONCLUSION: Almost 70 per cent of vaccinees at 9 months of age had seroconversion to measles vaccine with GMT of 1:14.8 while fifty three per cent of 18 month old children had an average GMT of 1:8.2. The GMT of the two groups was significantly different (p < 0.05). At 4 years of age almost all the children had NT antibody to measles with a GMT of 1:73.8 (p < 0.05) Vaccine failure is likely to be one factor responsible for the high incidence of measles after the introduction of measles vaccine into the Expanded Program of Immunization (EPI). The authors suggest giving a booster dose of measles at 15 months of age to boost the antibody level before waning of measles antibody at 18 months old, in order to protect this group of children from contracting measles.