The success of specific prophylaxis of diphtheria is undeniable. This infection has been reported sporadically or completely absent worldwide, provided vaccination coverage of children and adults of decreed age reaches or exceeds 95%. Nevertheless, the diphtheria prophylaxis is still relevant, since from 4.000 to 7.000 cases are registered annually worldwide according to WHO. Serological testing performed in different age groups and being a part of diphtheria surveillance in our country allows us to evaluate the quality of vaccine prophylaxis and identify potential risk groups that have no protection against this infection.
OBJECTIVE
Assessment of the timing appropriateness of the next scheduled adult revaccination and determination of the risk group for diphtheria incidence based on the serological testing of anti-diphtheria immunity in indicator groups in Russia in 2013-2016.
MATERIAL AND METHODS
The analysis of the anti-diphtheria immunity status in the Russian Federation in 4 indicator age groups (30-39, 40-49, 50-59, 60 years and older) carried out in 2014-2016 in compared with 2013 (before vaccination) was used as the basis for assessing the efficacy of the next scheduled adult revaccination. Three criteria were used: a decrease in the percentage of unprotected (seronegative) subjects, an increase in the percentage of high serum antibody titers subjects (1:320 or higher), and the level of actual protection of subjects in each age group (the number of subjects with protective titers of diphtheria antibodies). According to serological testing reports of anti-diphtheria immunity, 109.295 sera samples were analyzed. Anti-diphtheria antibodies in serum were determined using a passive hemagglutination test. A serum dilution of 1:20 or higher was considered as the protective level of antibodies.
RESULTS AND DISCUSSION
Analysis of serological testing results of anti-diphtheria antitoxic immunity in 2013-2016 showed that the average changes of all criteria for assessing the efficacy of the next scheduled diphtheria revaccination was insignificant in the studied indicator groups of adults in Russia. However, the age groups 50-59 years and 60 years and older showed a higher percentage of seronegative subjects than the other age groups (7.1±0.30% and 10.3±0.42%, respectively). However, since 2013-2016 the epidemiological insecurity indicator (10% or more subjects with no antibodies to diphtheria) is recorded annually in 15-25 regions in these age groups, which confirms that they remain risk groups. In 43.4% of all examined individuals from all regions of our country in all indicator groups, there is no improvement in the estimated figures of the next scheduled revaccination efficacy of adults. A significant increase in the percentage of seronegative subjects and a decrease in the percentage of high antibody titers subjects are observed by 2016 in three age groups (30-39, 40-49, and 50-59 years). The highest rates, indicating the absence of the next scheduled revaccination, were recorded in the age group 60 years and older.
CONCLUSION
According to serological testing data, diphtheria revaccination was was poorly performed during the analyzed period in the age groups of 50-59 years and 60 years and older. Consequently, the coverage of the regions of our country conducting proper serological testing (objectively determining the percentage of susceptible to diphtheria subjects) among vaccinated subjects aged 60 and over does not reach 90%.
