Evaluation of maternal measles antibody titers and response to the measles vaccination at the age of 9 months in preterm infants

Abstract

An analysis of lower seroconversion rates and decreased vaccine efficacy, probably due to immature states of immune systems, was conducted by the Turkish Ministry of Health to propose a new strategy of vaccination against measles (at the age of 12 months by ROR vaccine instead of a measles vaccine at the age of 9 months). In this study, we aimed at evaluating whether this strategy, which has been followed by most of the developed countries, was justified for term and especially preterm infants by evaluating their maternal measles antibodies (MMA) titration and seropositivity rate at the age of 9 months and also their responses to measles vaccination at that age. A prevaccination venous blood sample was taken just before the vaccination and postvaccination blood samples 8–10 weeks after the vaccination by 0.5 ml Schwarz-strain live-attenuated measles vaccine (Pasteur, Paris, France). Measles Ig G kits (Gull RBU-100, Gull Lab. Salt Lake City, Utah) were used to study the measles antibody titers. The mean value of reference serum and the serum samples with REU (relative Elisa unit) values greater than 1 were accepted as positive. The characteristics and results for three groups are presented in Table 1. While no significant difference was found between the prevaccination values of group I and II, a statistical significance was detected for group I versus group III. Postvaccination values had a statistical significance for group I and II versus group III. For all groups, the differences between prevaccination and postvaccination mean REU values were found to be significantly higher. MMA seropositivity rates at the age of 9 months were 4.5% in group I, 19% in group II, and 21% in group III. In one of our previous studies, although no significant difference was detected between the maternal REU values in preterm and term groups, the cord blood samples showed a lower titer of mean REU values in preterm infants [2]. At 6 months, seronegativity increased to 86% and 74% for premature infants born at gestational ages ≤32 weeks and >32 weeks, respectively. WHO reports that the ideal timing for vaccination is the age when the MMA seropositivity rate drops under 5% in the population, in order to get a satisfactory response to the vaccination [1]. The results of this study were in favor of the new measles vaccination strategy at the age of 12 months in our country. But our results would suggest continuing to vaccinate group I babies who were born before 32 weeks of gestational age, but not later than the age of 9 months. This suggestion is especially valid in developed countries where most of the mothers are immunized by vaccination. Since passively acquired maternal measles antibodies might be expected to be lower among infants whose maternal immunity is vaccineEur J Pediatr (2007) 166:1181–1182 DOI 10.1007/s00431-006-0361-3