Evaluation of age-related distribution of measles cases with primary and secondary immune response in Russian Federation, 2010-2016
In 2010-2016, blood serum samples were examined from 5539 patients, aged < 1-60 years, with clinically and laboratory confirmed measles. Primary or secondary type of immune response was determined for all measles cases. Studies were performed with children aged < 1-14 years (2381), adolescents, 15-17 years old (189), and adults aged 18-60 years (2969). Serum measles-specific IgM antibodies were measured by “VektoKor’ IgM” ELISA test system (Russia), concentration and avidity of specific IgG - by using “Anti-Measles Viruses ELISA/IgG” and “Avidity: Anti-Measles Viruses ELISA/ IgG” (Euroimmun, Germany). Primary immune response was identified based on the presence of serum measles-specific low avidity IgM and IgG antibodies, whereas secondary immune response was characterized by detecting high avidity IgM and IgG antibodies at concentration of ≥ 5.0 IU/ml. Analyzing measles-specific IgM antibodies in 2010-2016 demonstrated that measles morbidity was mainly due to children, aged 1-2 years reaching up to 39.9% of the total number of children with measles aged < 1-14 years as well as adults aged 18-40 years old comprising as high as 80.1% total number of patients aged 15-60 years. Serum measles-specific IgG testing showed that in 15.0% of cases they were detected at concentration of ≥ 5.0 IU/ml. Further serum dilution resulted in finding IgG titer ranging within 8.5-45.0 IU/ml (21.4+0.36) and high avidity antibodies in 80-100% (92.5+0.2) cases. The remaining 85.0% cases found low avidity measles-specific IgG antibodies (< 30%) at concentration of 0.2-3.46 IU/ml (1.73+0.03). An age-related analysis of our data demonstrated that all children under 14 with laboratory-confirmed measles developed primary immune response. Moreover, in 73.7% of measles patients aged 15-60 with primary immune response measles might be prevented by timely vaccination, whereas persons with “vaccine failure” comprised 26.3%. In 2010 (0.09 per 100,000 subjects) and 2016 (0.12 per 100,000 subjects), frequency of patients with “vaccine failure” during relative epidemic well-being was 35.3% and 18.2%, respectively, exceeding 9.9% (p < 0.001) serving as a hallmark 2014 high measles incidence rate (3.24 per 100,000 subjects).The data obtained indicate that measles virus circulate among people with “vaccine failure,” which may account for potential to spread and infect unprotected population cohorts as well as cause measles outbreaks during periods of epidemic well-being.