Background Iranian children were vaccinated with the scheduled two doses of monovalent measles vaccine (mMV) from 1984. In December 2003, a nationwide campaign of measles-rubella (MR) immunization was established to vaccinate 5–25 year- old individuals. In 2004, the mMV was replaced with measles- mumps- rubella (MMR) vaccine. Despite the high vaccination coverage, the outbreaks of measles still occur in the country. In this Study, the MR immunity status of various age groups, vaccinated with different schedules was investigated, and the immunologic response of seronegative subjects to revaccination was examined. Methods This cross-sectional study was conducted among 7–33-year-old healthy individuals with a documented history of measles vaccination from November 2017 to June 2018. The subjects were categorized as follows: group A, including 20–33 year-old individuals; vaccinated with 1–2 doses of mMV at ages 9 and 15 months, and revaccinated with MR, group B, including 15–19-year-old individuals, vaccinated with two doses of mMV at 9 and 15 months of age, and received additional dose of MMR upon school entrance, group C, including 11–14 year-old individuals, vaccinated with two-doses of MMR at the ages of 15 months and 6 years, and group D, including 7–10 year-old individuals vaccinated with two-doses of MMR vaccine at the ages 12 and 18 months, respectively. Levels of antimeasles- antirubella IgG antibodies in the collected sera were measured. Also antimeasles- antirubella IgM and IgG of seronegative individuals were reexamined at 4–6 weeks after MMR revaccination. The collected data were analyzed using descriptive statistical methods. Results A total of 635 individuals were investigated in this study. Group A, 98; group B, 295; group C, 139; and group D, 103 persons. Overall, 12.3 and 18.4% of the population were seronegative for measles and rubella antibodies. This rate varied greatly between the 4 groups: group A, 0/0–2%; group B,15.2–25.0%; group C,11.5–17.2%; and groupD,14.6–18.4%. After revaccination, 92 and 94.9% of seronegative individuals showed IgG response to measles and rubella vaccines, respectively. Conclusion Despite the high coverage rate of M-R containing vaccines, a significant number of vaccinated subjects were seronegative for measles and rubella, possibly because of secondary vaccine failure; this may negatively affect measles-rubella elimination targets in the country. If these findings are confirmed in similar future studies, a more robust regional/national supplementary immunization activity will be considered.

Background. Despite high rate of vaccination coverage with 2-doses of measles vaccine among Iranian children, outbreaks of measles occurred among different age groups and fully vaccinated subjects. Although the main reason for these outbreaks is unknown, however, vaccine failure was supposed to be an important cause. This study was designed to determine the immunogenicity of measles- mumps- rubella (MMR) vaccine currently in use among Iranian children.Methods. This prospective study was conducted among ³ 12 month- old healthy children who were candidates of scheduled MMR vaccination. Blood samples were obtained from each mother- infant pair just before vaccination, and from infants 4- 6 weeks after MMR1 and MMR2 immunization. Collected sera were tested for specific lgG antibodies against MMR agents using ELISA method. The proportion of seroprotected subjects among mother- infant pairs before vaccination as well as the prevalence rates of seroconversion after MMR1 and MMR2 vaccination were calculated. Collected data were analyzed using descriptive statistical methods.Results. During 22-months study period, 92 mother- infant pairs were participated. Seroimmunity rates against MMR viruses were 85.8%, 84.7% and 86.9% for mothers, and 3.2%, 2.1% and 1.0% for children, respectively. After MMR1 vaccination of 52 seronegative children, 80.7%, 78.8% and 75% were seroconverted. These rates increased to 94.8%, 89.7% and 92.3% after the MMR2 vaccination. Also, the specific immunity was enhanced among seropositive children.Conclusion. Majority of the mothers and few infants were immune to MMR viruses, prior to MMR1 vaccination. Seroconversion rates detected after MMR1 injection, and overall seroprotection rates achieved after 2-doses of MMR vaccination were less than expected and inadequate to preserve long-term protection against MMR agents.