Epidemiological and serological investigations of vaccine-preventable diseases and their implications for vaccination policy in the Lao People's Democratic Republic

The Lao People’s Democratic Republic (PDR) is a landlocked country in South-East Asia. Founded in 1975 by the Lao People’s Revolutionary Party, the Lao PDR of today is a relatively young nation. The Expanded Program on Immunization of the World Health Organization was established in the country in 1979. Starting with a limited vaccination schedule including six vaccines (Bacillus Calmette-Guerin, Diphtheria, Tetanus, Pertussis, Polio, and Measles vaccine), the programme was extended during the following years and now also includes vaccines against hepatitis B virus, rubella virus, pneumococcal disease, Japanese encephalitis virus and human papilloma virus. The Expanded Program on Immunization is generally considered as one of the most successful health programs in the Lao PDR but still faces many challenges. This research thesis describes my serological and epidemiological investigations of vaccine-preventable diseases and vaccination efforts in the Lao PDR with the aim to inform vaccination policy. Specifically, the overall objectives of this research work are to (i) characterize the epidemiology of vaccine-preventable diseases for which there is no routine vaccination, to (ii) assess the level of protection against vaccine-preventable diseases and investigate possible risk factors for seroprotection and (iii) evaluate the impact of vaccination on disease prevalence. The overall objectives were broken down into smaller research questions addressed in six research articles and one review article presented in the thesis. Three of the presented articles were already published in peer-reviewed journals. In the first two articles, serological testing was used to establish baseline data for the prevalence of Haemophilus influenzae type b and Salmonella enterica, subspecies enterica serovar Typhi in the Lao PDR in absence of routine vaccination. The data may serve as reference for follow-up studies and/or as complementary data to clinical data. Serological data was used to assess the level of population immunity in children after routine childhood vaccination with the pentavalent Diphtheria-Tetanus-Pertussis-Hepatitis B-H. influenzae type b vaccine and the measles and rubella vaccine. The studies highlighted the progress made but also identified predictors associated with suboptimal vaccination rates in Bolikhamxay, a central province in the Lao PDR. Furthermore, the timeliness of the vaccination was assessed and factors associated with delayed vaccination were identified. The last two research articles dealt with the epidemiology of hepatitis B in the Lao PDR. A literature review was conducted to give an overview over the current data situation of hepatitis B prevalence in the country. In addition, a study with the aim to investigate the serological hepatitis B profiles among adolescents born before and after the introduction of the hepatitis B vaccination was conducted. In summary, the data presented in this thesis contribute to the understanding of vaccine-preventable diseases in the Lao PDR, provide information regarding the vaccination efforts in the country and the progress which has been made in the past years. The findings of these studies were translated into vaccine policy recommendations which were communicated to local public health authorities.