Seroprotection at Different Levels of the Healthcare System After Routine Vaccination With Diphtheria-Tetanus-Pertussis whole cell-Hepatitis B-Haemophilus influenzae Type B in Lao People's Democratic Republic

Abstract

Background: The Lao People's Democratic Republic continues to sustain a considerable burden of vaccine-preventable diseases because of incomplete vaccine coverage and weak vaccine responses. We have assessed seroconversion after routine vaccination with the pentavalent vaccine to capture weaknesses of vaccine management at the different levels of the healthcare system.

Methods: A total of 1151 children (aged 8-28 months) with 3 documented doses of the pentavalent vaccine delivered at central hospitals in Vientiane and the provincial hospital, 3 district hospitals, and 10 health centers in Bolikhamxay province were enrolled. Sociodemographic information was collected with a standardized questionnaire. Serum samples were analyzed for antibodies against vaccine components, and bivariate and multivariable analyses were performed to identify risk factors for low vaccine responses.

Results: Seroprotection rates at the provincial, district, and health center level were as high as in central hospitals, but seroprotection rates in areas covered by remote health centers were significantly lower. Protective levels also rapidly decreased with age at sampling. Seroprotection rates in Bolikhamxay against the different components reached 70%-77% and were up to 20% higher than in previous studies in the same region; 18.8% more children received the hepatitis B vaccine birth dose and the hepatitis B virus infection rate was 4 times lower.

Conclusions: Vaccine immunogenicity has dramatically improved in a central province, likely due to training and investment in the cold chain. Nevertheless, there remains a need to focus on the "last mile" in remote areas were most children are vaccinated through outreach activities.

Keywords: diphtheria; hepatitis B; immunogenicity; tetanus; vaccination.

Figure 1.

Seroprotection against diphtheria (A), tetanus (B), hepatitis B (C), Hib (D), and pertussis (E) according to place of vaccination in children aged 8–23 months grouped into 3 age ranges at the time of sample collection: 8–12 months, 13–17 months, and 18–23 months. Results are displayed with 95% confidence intervals. Only those children who were vaccinated with all 3 doses by the same immunization service either at a central hospital (CH) in Vientiane, the provincial hospital (PH), the district hospitals (DHs), or the health centers (HCs) were included in the graph. The HCs in the study in Bolikhamxay were further grouped according to travel time to the DH during the rainy season. Immunity was considered protective as described in methods. Seroprotection rates of children aged 13–17 months and 18–23 months at all healthcare facilities combined were compared to the youngest age group (8–12 months). Seroprotection rates between places of vaccination were always compared to the same age group at the CH. Abbreviations: B. pertussis, Bordetella pertussis; HCF, healthcare facility; HBV, hepatitis B virus; H. influenzae b, Haemophilus influenzae type b; H. influenzae, Haemophilus influenzae. *P ≤ .05, **P ≤ .01, ***P ≤ .001, ****P ≤ .0001.

Figure 2.

Comparison of the serological profiles of children aged 8–28 months enrolled in Bolikhamxay Province in 2017 and 2013/2014. Seroprotection rates are displayed with 95% confidence intervals. Immunity was considered protective as described in methods. Abbreviations: anti-HBs, anti–hepatitis B surface antigen; anti-HBc, anti–hepatitis B core antigen; anti-Hib, anti–Haemophilus influenzae type B. ****P ≤ .0001.