ABSTRACT
Measles is a vaccine preventable infectious disease. Despite the widespread availability of an effective measles vaccine, number of measles cases is noticeable in Iran. Because measles-specific antibody titer after vaccination is lower than after natural infection there is a concern that vaccinated persons may gradually lose protection from measles. To examine the persistence of vaccine induced antibody, participants with documented history of vaccination were assessed to determine the sero-prevalence and titer of measles antibody. This study was carried out in Urmia- Iran. Documented history of at least a single dose of live attenuated measles vaccine [at 9 or 15 month of age] was necessary to be included. Blood was collected from 840 subjects between 5-25 years old. The sera were tested for anti-measles IgG antibodies, by ELISA [IBL Germany]. Associations between predictive factors such as demographic data, vaccination status [once or twice] with IgG sero prevalence in routine vaccinated subjects were investigated by logistic regression analysis. The antibody titers in 54.76% of cases were in the range of protective level [IgG> 12IU]. The mean of antibody was significantly increasing after the 16[th] year of life The antibody titers were higher in participants who received one dose of measles vaccine in comparison with the persons who were immunized with two doses of measles vaccine. Antibody titers were slightly higher in men than in women. On multiple logistic regression analysis, of all variables examined, only vaccination status retained a significant association with anti measles sero-positivity rate [estimated odds ratio 0.395 n<0.05]. Elevation of antibody titer many years after vaccination is most likely due to boosting effect from repeated exposure to circulating wild virus resulting in unapparent or sub-clinical reinfection. This group of persons would be the most likely to support viral transmission in the absence of disease