Analysis of surveillance results of measles vaccine quality and success rates of immunization in Zhejiang province  2004-2007

Objective To identify the cause of high incidence of measles in Zhejiang from 2004 to 2007.Methods The results of surveillance of measles vaccine quality and the success rate of immunization in Zhejiang province from 2004 to 2007 were analyzed.Fixed-point and linear approaches were employed in the surveillance of measles vaccine quality; and the success rate of immunization was determined by measuring the difference between the measles antibody levels before and after immunization among 8-month-old children.Results Thirty-one batches of measles vaccines collected from the central cold storage of Zhejiang Center for Disease Control and Prevention were qualified, the titer being (3.16 0.25) log TCID50/0.1 ml; 47 measles vaccines collected from the town- and county-level, municipal and provincial monitoring sites were qualified, the titer being (3.04 0.32) log TCID50/0.1 ml, and no statistically significant difference was shown among the monitoring points at all levels.Measles vaccination for 8-month-old children would ensure 95% of the children protective antibodies; the higher the pre-immunization antibody levels, the lower seroconversion rate after immunization.Conclusion Measles vaccines applied in Zhejiang province from 2004 to 2007 achieved a protective potency with favorable primary immunization effects.It is thus not considered to be the major cause for high incidence of measles in recent years.Subsequent surveillance of the quality of measles composition-containing vaccines and the success rate of immune is required.