Introducing New Vaccines in Developing Countries: Concepts and Approaches to Estimating Burden of Haemophilus Influenzae Type B-Associated Disease

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INTRODUCTION

During the past several decades, a number of new vaccines have been introduced into the routine immunization programmes of developing countries starting with the earliest efforts of the World Health Organization (WHO) in the global smallpox-eradication campaign and the establishment of the Expanded Programme on Immunization (EPI) (1). During the 1970s-1980s, as developing countries introduced routine infant immunizations, immunizations, there was little doubt among international health officials and national public-health decision-makers that the basic childhood vaccines, already available in developed countries for 20 or more years, were desperately needed to reduce morbidity and mortality among infants and children (2,3).

Following the development and routine introduction of new vaccines for hepatitis B and Haemophilus influenzae type b (Hib)-associated disease in developed countries, the use of these new vaccines in developing countries was felt to be a natural next step (4,5). However, the introduction of these vaccines has lagged behind their introduction in developed countries by more than 10 years (6). A number of countries still do not use hepatitis B vaccine as a routine immunization, and a good number of developing countries have yet to begin Hib immunization. In the case of hepatitis B vaccines, a number of factors associated with delayed introduction have been identified, including problems with knowledge of disease burden, cost of vaccines, supply of vaccines, and immunization programme logistics of delivering an increasing number of vaccines to infants (7).

The experience over the past 20 years with hepatitis B and Hib vaccines has underscored the need for understanding the degree to which new vaccine-preventable diseases are a problem for a given population. This knowledge allows decision-makers to place a given disease in the overall context of national public-health problems. This process of understanding the extent of a particular disease problem requires effort to establish the burden of disease.

BURDEN OF DISEASE

In general, the burden of disease is represented by the sum total of outcomes that include both morbidity and mortality associated with a particular pathogen or disease (8). Thus, the burden for a number of pathogens, such as Hib, requires consideration not only of potential outcomes, e.g. hospitalizations, but recognition that Hib is capable of causing different disease manifestations (9). Thus, to account for the impact of Hib in children, we consider moderate or severe manifestations of invasive Hib disease, e.g. meningitis, pneumonia, and sepsis, that may lead to emergency visits, hospitalizations, clinical sequelae, or death (10).

Prior to the introduction of Hib vaccine in developed countries, Hib-associated deaths were frequent (11). In developing countries where access to healthcare is limited, Hib-associated mortality is thought to be high. Previous studies in several countries have shown that the highest number of Hib-associated deaths occur among children aged less than five years, especially among children aged less than two years (12,13). In addition to death, children who survive serious disease, such as Hib meningitis, are often affected by lifelong disability due to permanent damage of the central nervous system that leads to neurologic deficits (14). Such disability may lead to physical or cognitive deficits. Other severe manifestations include meningitis, pneumonia, and sepsis, and may require emergency department treatment or hospitalization.

Because of these severe disease manifestations and their associated outcomes, accurate estimation of the burden of invasive Hib disease in studies can provide important insights for health policy-makers who must make important choices regarding public-health interventions that will be financed with public or international donor funds. Appropriately-conducted burden-of-disease studies often provide previously unavailable data that show the relative importance of diseases. …