Measles and Rubella Serosusceptibity among Population Vaccinated with Different Schedule of Vaccination: the potential impact on measles elimination in Iran.

Abstract Background: In addition to scheduled 2-doses monovalent measles vaccine (mMV) immunization of Iranian children since 1984, a nationwide campaign of measles-rubella (MR) immunization among 5- 25 years-old population in December 2003 was conducted. From 2004 mMV was replaced with measles- mumps-rubella (MMR) vaccine. Despite a high vaccination coverage, outbreaks of measles occurred in the country. Study was designed to investigate seroimmunity status against measles and rubella among various age groups of population who were vaccinated with different schedule since 1984. Also, immunologic response to revaccination in seronegative subjects was evaluated. Methods: From 1 November 2017 to 30 June 2018 a cross- sectional study among 7- 33 year old (born 1984-2011) healthy population with documented history of measles vaccination was conducted. Based on their age and history of vaccination status categorized as GA: 20-2333 years old; vaccinated with 1-2 dose of mMV, and also MR revaccinated. GB: 15-19 years, vaccinated only with 2- doses of mMV at the ages of 9 and 15 months and MMR 2-5 years later. GC: 12-14 years and GD: 7-11 years; vaccinated with 2- dose of MMR vaccine at the ages 15 months - 6 years, and 12-18 months respectively. Collected sera were assessed to measure antimeasles and antirubella IgG antibodies concentration. Four to 6 weeks after revaccination of seronegative subjects, antimeasles-antirubella IgM and IgG antibodies were rechecked. Collected data were analyzed using descriptive statistical methods.Results: Totally 635 individuals, 312 female were included. Relative distribution of subjects in each group was as: GA: 98, GB: 295, GC: 139, and GD: 103 persons. Overall, 12.28% and 18.4% of population were soronegative, and varied greatly between groups: 2%-0/0%, 15.2%- 25.0%, 11.5%- 17.2%; and 14.6%-18.4%, to measles and rubella, respectively. After revaccination, 92% and 94.9% showed 1gG response to measles and rubella vaccine respectively.Conclusion: Despite high coverage rate with measles and rubella containing vaccine, a significant numbers of vaccinated subjects lost their seroprotection were seronegative, possibly because of secondary vaccine failure. This may affect measles-rubella elimination goal in the country. If these data were confirmed by further studies, more strengthen regional/ national supplementary immunization activity should be considered.