Analysis of a Serological Study of Pertussis among Children and Adolescents in the Republic of Kazakhstan

Relevance. In 2018 over 151 000 cases of whooping cough were reported worldwide. In the Republic of Kazakhstan the incidence of whooping cough has always remained relevant. The incidence is recorded mainly among children under 14 years of age, whose share is 96–100% of the total incidence in certain years. It should also be noted that 82,9–96% of sick people are not vaccinated against whooping cough. Aims. Assessment of the duration of protection after vaccination against pertussis infection in Kazakhstan using antibodies against pertussis toxin (PT) and (IgA and IgG) as a specific marker of pertussis infection or vaccination in children and adolescents in the cities of the Republic of Kazakhstan: Aktobe, Karaganda, Taldykorgan, Shymkent for evaluation appropriate age for booster vaccination. Materials and methods. For the study included medical organizations in the cities of Aktobe, Karaganda, Taldykorgan, Shymkent. Participants aged 10–14 years who were hospitalized in children's hospitals and 15–18 years old who visited polyclinics were invited to participate in the study. Each city has 1 children's hospital (4 in total) and 2 polyclinics (8 in total). A total of 520 people of different age groups participated. Study period: February 2021 – October 2021. Inclusion criteria were such aspects as: age from 10 years to 18 years 11 months 29 days, informed consent obtained from parents or guardian(s) and patient consent, enrollment after visiting the clinic, the presence of documented evidence of immune status. An association between two qualitative variables is considered statistically significant if the p-value calculated using     the Chi-squared test is less than 0.05. Results. Among 520 participants aged 10–14 years – 200 (38.5%) and 15–18 years – 320 (61.5%), including boys – 284 (54.6%), girls – 236 (45.4%). The largest number of study participants was aged 15, 16 and 17 years, 10 participants (1.9%) had periods of prolonged coughing in the past 6 months. The first, second and third pertussis vaccines were received by 100% of children. The first and second vaccine for all children was the Adsorbed Diphtheria-Tetanus-Pertussis Vaccine (DPT). The third vaccine for 519 children was also DPT, for one child – AbDPT, due to the transition to a cell-free vaccine from the second half of 2013. The additional vaccine scheduled at 18 months of age was given to 519 participants (99.8%), of which 517 children (99.6%) received DPT and two children (0.4%) DPT. Just over half of the children (276 or 53.1%) also received the whooping cough vaccine at age 6. In biological blood samples of 17 participants (3.3%). antibodies of the IgA class were detected in 245 samples (47.1%) – antibodies of the IgG class. Of the 17 participants with IgA antibodies, 15 also tested positive for IgG. In total antibodies of the IgA and IgG classes were detected in 247 participants which amounted to 47.5%. Conclusions. This study showed the duration of protection after pertussis vaccination in Kazakhstan among different age groups. In total, antibodies of the IgA and IgG classes were detected in 247 participants out of 520 which amounted to 47.5%. IgA antibodies were detected in biological blood samples in 17 participants (3.3%), IgG class antibodies in 245 samples (47.1%). The prevalence of IgA antibodies was statistically significantly higher among older children and among children who had respiratory symptoms in the 6 months prior to the study. The prevalence of IgG antibodies was statistically significantly higher among children vaccinated against whooping cough at the age of 6 years (47.1%) and at the age of 10–14 years (56.2%) than in the age group of 15–18 years (43.8%) and also significantly higher among those, who share a bedroom with other family members compared to children living in separate rooms. Thus an increase in whooping cough and a decrease in protective vaccine immunity among older age groups can be stated which raises concerns about transmission of the infection in the home to vulnerable children and the need to strengthen vaccination strategies.