Measles and Rubella Serosusceptibity among Population Vaccinated with Different Schedule: The potential impact on Measles-Rubella elimination in Iran.

Abstract

Background: Iranian children have been vaccinated with the scheduled two doses of monovalent measles vaccine (mMV) since 1984. In December 2003, a nationwide campaign of measles-rubella (MR) immunization targeted 5-25 years population was established. In 2004, the mMV was replaced with measles- mumps-rubella (MMR) vaccine. Despite the high vaccination coverage, the outbreaks of measles still occurs in the country. In this Study, the measles-rubella 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 fallow: groupA: including 20-33 years-old; vaccinated with 1-2 dose of mMV, and revaccinated with MR, groupB, including 15-19-year-old individuals, vaccinated with two doses of mMV at nine and 15 months of age, and in addition to one dose MMR upon school entrance, groupC, including 11-14 year-old individuals vaccinated, with two-doses of MMR at the ages of 15 months and six years, and groupD, including 7-10 year individuals vaccinated with two-doses of MMR vaccine at the ages 12 and 18 months, respectively. Nest the consecrations of antimeasles-antirubella IgG antibodies in the collected sera were measured. Among seronegative subjects, the antimeasles-antirubella IgM and IgG were reexamined at 4-6 weeks after MMR revaccination. The collected data were analyzed using descriptive statistical methods.Results: A total of 635 individuals, including 322 females were investigated in this study. The relative distribution of subjects in each group was as falows: groupA, 98; groupB, 295; groupC, 139; and groupD, 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: groupA, 2%-0/0%; groupB,15.2%- 25.0%; groupC,11.5%- 17.2%; and groupD,14.6%- 18.4%. After revaccination, 92% and 94.9% of seronegative individuals only showed IgG response to measles and rubella vaccines, respectively.Conclusion: Despite the high coverage rate of M-R containing vaccines, a significant numbers 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 should be considered.