Serological Response to Measles Revaccination in a Small Population After a Mass Measles Revaccination Program

Abstract

Background: In spite of vaccination, outbreaks of measles occur in many countries, and measles remains the most frequent cause of death among vaccine preventable diseases. Objectives: To compare anti-measles antibody titer between revaccinated and non-revaccinated medical students 2 years after the National MR (Measles, Rubella) Vaccination Program, which was implemented in 2002-2003 for individuals aged 5 to 25 years in Iran. Patients and Methods: This stratified cross-sectional study was conducted on 78 revaccinated and unvaccinated for national MMR vaccination (2002) medical students aged 22-25 years, who attended our Markaz Tebi Children Hospital in Tehran for their pediatric rotation from summer to winter in 2005. The revaccinated group was selected by simple random sampling from a list of names of the students and the non-revaccinated group included all the non-revaccinated students. Serum IgG and IgM anti-measles antibody titers of the subjects were measured using indirect enzyme-linked immunosorbent assay (ELISA), and the levels were compared between the 2 groups of students. Data were analyzed using chi square test and independent samples t test. Statistical significance was defined as P values of < 0.05 by SPSS ver.13 Software. Results: Overall, we recruited 45 subjects with a mean age of 23.7 ± 0.12 years in the revaccinated group and 33 subjects with a mean age of 24 ± 0.25 years in the non-revaccinated group (P = 0.2). The mean anti-measles IgG antibody titer was 31.8 ± 21.2 IU/mL (range, 1-190 IU/mL) in the revaccinated group and 6.12 ± 8.8 IU/mL (range, 1-45 IU/mL) in the non-revaccinated group (P < 0.001). The mean anti-measles IgM antibody titers were 2.6 ± 6.7 IU/mL (range, 1-45 IU/mL) and 1 ± 0 IU/mL (range, 0-1 IU/mL) in the revaccinated and non-revaccinated groups, respectively (P = 0.1). Anti-measles IgG was present (serum titer ≥ 13 IU/mL) in 46.7% of the individuals of the revaccinated group and 6% of the individuals of the non-revaccinated group (P < 0.001). Conclusions: The results of this study indicate that although the percentage of individuals with protective levels of anti-measles antibody increased to 46.7% after revaccination, the protection was inadequate in more than 50% of vaccine recipients, thereby, emphasizing the need for checking antibody levels after revaccination.