Academic journal article Bulletin of the World Health Organization

Report of the Workgroup on Viral Diseases

Academic journal article Bulletin of the World Health Organization

Report of the Workgroup on Viral Diseases

Article excerpt

Introduction

The Workgroup identified measles, rubella, and viral hepatitis B as priority candidates for eradication. Viral hepatitis A is not recommended for elimination or eradication at the present time. Yellow fever, rabies, and Japanese encephalitis cannot be eradicated because they are found in animal reservoirs, but they can be controlled, in some cases to the point of elimination, through immunization programmes.

The group used the definitions of eradication and elimination adopted by the Dahlem Workshop on the Eradication of Infectious Diseases. Elimination refers to reducing the incidence of a disease to zero within a defined geographical area, with continued intervention measures as needed, while eradication refers to permanently reducing the incidence of a disease to zero worldwide, with no intervention measures required.

Viral hepatitis A and B

Viral hepatitis A

Hepatitis A virus (HAV) infects more than 80% of the population of many developing countries by late adolescence, and is common in developed countries as well (1-3). It produces a generally asymptomatic infection in under-5-year-olds, and an acute, self-limited disease in older children, adolescents, and adults (1, 4).

Inactivated HAV vaccines, which only became commercially available in 1994, effectively confer protection in more than 95% of vaccinated persons (2, 5, 6). Routine vaccination of children aged [is greater than] 2 years has effectively interrupted community-wide epidemics, and sustained vaccination has eliminated transmission of infection in these communities. While the potential for elimination of HAV exists, it cannot be recommended at this time, because of the impeding factors discussed below.

Essential facilitating factors. Routine childhood immunization with an effective, cell-culture-derived, inactive HAV vaccine has been shown to be cost-effective in populations with high rates of infection. The administration of the vaccine during community-wide outbreaks has been shown to be effective in interrupting transmission of the virus. The vaccine can also be administered with other vaccines and combined with other vaccine antigens (2).

Essential impeding factors. HAV vaccine is expensive, making large-scale purchases by developing countries difficult. Also, there is no vaccine formulation or schedule for use in infancy and early childhood, and it cannot be included in the Expanded Programme for Immunization (EPI).

Key strategies. It will be important to demonstrate the feasibility of eliminating HAV transmission in specific geographical areas. National acute disease surveillance must be improved to better differentiate viral hepatitis A from viral hepatitis B.

Research needs. Two areas of research are immediate priorities:

-- development of decision/economic models for hepatitis A vaccination in developing countries; and

-- development of vaccine formulations and schedules for infants and children [is less than] 2 years old.

Conclusions and recommendations. These are as follows:

-- eradication of HAV transmission appears to be both biologically and epidemiologically feasible;

-- the time required to achieve cessation of transmission may be short;

-- the coupling of HAV immunization with other vaccines appears to be feasible; and

-- population-based projects to demonstrate sustained elimination of HAV transmission should be initiated as early as possible.

Viral hepatitis B

Viral hepatitis B (HBV), which affects an estimated 360 million people worldwide, is a primary candidate for elimination or eradication. It occurs most often in Africa, the Pacific Islands, part of South America, most of Asia, and in ethnically defined populations in Australia, New Zealand, and the USA (7). Chronic infection, which usually begins in early childhood, is associated with risk of death from chronic liver disease, primarily as an adult, and with the risk of liver cancer, a leading cause of death among many adults in developing countries. …

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