Role Of Vaccination In Preventing Typhoid Fever: Experience From Vietnam

Background: Improvements in water and sanitation are essential to reducing the burden of many infectious diseases, most notably that of diarrhea and enteric fevers. Vietnam has considerable burden of enteric diseases including typhoid fever. The objective of this study was to retrospectively review epidemiological data on typhoid fever and environmental data that are often considered to be associated with typhoid fever in Vietnam over a period of 10 years from 1991 to 2001 to understand the trend and environmental risk factors of typhoid fever in Vietnam. Methods: Government of Vietnam collects data on typhoid fever by provinces. This government data was collected as part of the Existing Data Collection study under the Diseases of the Most Impoverished (DOMI) program of the International Vaccine Institute conducted between 1999 and 2007 and was retrospectively analyzed. In addition, the government provincial data on urbanization, water and sanitation status was compared for all provinces against incidence of reported typhoid fever and plotted in scatter diagram for the risk factor analysis. Retrospective data on typhoid vaccine coverage was collected from the National Institute of Hygiene and Epidemiology. Results: The annual incidence of typhoid fever in Vietnam varied over the first five years increasing from an incidence rate of 12/100,000 in 1991 to over 40/100,000 in 1995 and decreasing during the later five years from 35/100,000 in 1996 to 12/100,000 in 2001. There was seasonal variation with peak incidence from May to August. On the risk factor analysis for typhoid, urbanization, access to clean water, or access to sanitation were not statistically related to typhoid fever incidence. Conclusion: Based on the review of 10-year typhoid fever incidence data coinciding with the introduction of typhoid fever vaccine in Vietnam, improvement in water and sanitation alone did not appear to be significantly related to the reduction in the incidence of typhoid fever. The Government of Vietnam started typhoid vaccination in high-risk districts from 1997 which have contributed in reduction of typhoid fever in these districts. It is important to complement the preventive efforts with introduction of vaccines in the short to intermediate term to effectively control typhoid fever.