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

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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 nonrevaccinated
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 nonrevaccinated
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.

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