Routine immunization virtually eliminates major killer of young children in the Gambia

Jun 29 2005

The Lancet has today published online new research from a team led by the UK Medical Research Council's Richard Adegbola showing that routinely vaccinating infants against H. influenzae type b (Hib) - a bacterium that causes deadly diseases including pneumonia and meningitis - has virtually eliminated Hib meningitis in The Gambia.

The Gambian study shows that the vaccine is highly effective (94% efficacy with two doses) and that, even with moderate coverage and sub-optimal conditions, Hib vaccination can benefit all children because herd immunity is significant.

"Hundreds of thousands of young children are dying of Hib disease because of a lack of national Hib immunization programs," said Dr. Patrick Zuber of the Vaccines and Biologicals division of the World Health Organization (WHO). "This study proves that routinely immunizing children with Hib conjugate vaccine in developing countries is practical and will save lives - helping in the efforts to achieve a two-thirds reduction in the under-five mortality rate, a Millennium Development Goal."

"What makes this even more remarkable is that the virtual eradication of Hib disease has been achieved despite less than optimal circumstances," said lead study author Dr. Adegbola of the MRC. "There were interruptions in vaccine supply, less than 70% of children received the complete schedule of immunizations, and vaccine doses were often received late. This makes the Gambian findings particularly relevant to the real-life situation in other developing countries, especially in sub-Saharan Africa."

The study also showed that Hib carriage has also been virtually eliminated in The Gambia - in both vaccinated and unvaccinated children. Before vaccination 12% of children between one and two years old carried the infectious bacteria, now the rate is less than half of one percent and difficult to detect. The negligible carriage rates contribute to the herd immunity effect - unvaccinated children are protected because of reduced likelihood of transmission. This means that routine Hib conjugate vaccination is a highly effective way of preventing death and severe disability related to Hib disease in young children.

Prof. Orin Levine, Executive Director of GAVI's pneumococcal vaccine project, PneumoADIP said, "To nearly eradicate Hib meningitis from this area of Africa speaks volumes about the Gambia's program and the impact Hib vaccine will have on global health."

The WHO (which partially-funded the Gambian study) estimates that Hib causes 400,000-700,000 deaths each year - the majority of these deaths occur in children under five in the developing world. Children that survive Hib disease can be left severely disabled - bacterial meningitis can cause permanent deafness, seizures, or mental retardation. Before the introduction of a national vaccination program, The Gambia - like the rest of the developing world - had a high disease burden from Hib. Only 45% of Gambian children recovered fully from invasive Hib disease and 30% of those that contracted Hib meningitis died.

Routine Hib vaccination was introduced in The Gambia in 1997 as part of the country's expanded program on immunization (EPI). The new MRC/WHO study confirmed that since 2002 no cases of invasive Hib disease have been detected. Before any use of the vaccine the annual incidence of Hib meningitis alone was over 200 per 100,000 children under 12 months of age and 60 per 100,000 in children younger than five.

The study's supporters hope that these results drive countries in sub- Saharan Africa that have not yet introduced Hib vaccination to do so, and encourage those that have done so to sustain their efforts.

"The results of the Gambian study are incredibly encouraging because they show that elimination of Hib disease is achievable," said Julian Lob-Levyt, Executive Secretary of the Global Alliance for Vaccines and Immunization (GAVI). 'What is needed now is a dedicated effort to ensure the rapid adoption of national Hib immunization programs throughout the developing world to reduce the burden of death and disability associated with this disease."

http://www.who.int and http://www.mrc.ac.uk/