A survey of examining herd measles immunity in adults over 35 years old

A high measles incidence rate has been registered in Russia in recent years, with adults being actively involved in the epidemic process (about 40% of patients), thereby underlying relevance of assessing herd immunity in different  age groups to measure its risk. The data on examining serum antibodies to measles virus in 402 residents of Petrozavodsk are shown: 164 and 238 subjects were born in 1948–1968 (51–71 years) and 1970–1983 (36–50 years), respectively. It was found that the second group had significantly higher percentage not only of seropositive persons (94.1±1.5 vs. 77.4±3.3%, respectively), but also frequency of detected high IgG level (5 and more IU/l) reaching 39.7±3.5 vs. 15.4±5.8%, respectively. Analysis of vaccination history showed that of 351 people with protective antibody levels, 20.9% were vaccinated once or twice, 14 of them in childhood and 63 within the 15 years prior to the study. Of the 51 people with no measles antibodies or below protective level, 13.7% were vaccinated: five in childhood, and two within the last 15 years. Among those who was born in 1948–1968, 87.1±2.2% provided no information about previous vaccinations and probably were not vaccinated. In this group, percentage of those examined with a protective antibody level was significantly higher than in the 36–50 years group — 87.1±2.2 and 62.2±4.3%, respectively. In addition, 23 subjects confirmed that they recovered after measles in childhood. Of these, antibodies were detected in 21 subjects, including 9 having serum titer at level of 5 or more IU/ml. Until 1969, the Republic of Karelia registered a high level of measles morbidity (477–2176,0 per 100 thousand). The predominance in the group born before 1969, individuals seropositive to measles mainly at high titer, indicates that intense post-infectious immunity was preserved. The lack of protective level of antibodies to measles virus in 22.6% of persons aged 36–50 years (1969–1983 year of birth), due to the low level of post-infectious and insufficient durability of post-vaccination immunity allowing to definer them as a high risk group for measles infection.