Seasonal meningococcal A epidemics in Africa’s "meningitis belt" could become remnants of the past if the introduction of a new and affordable conjugate polysaccharide vaccine meets the high expectations of the many people and organizations that collaborated to produce it.
In early December of last year, the West African nation of Burkina Faso became the first country to implement a nationwide program to immunize individuals aged 1-29 years with the vaccine, called MenAfriVac. The start of the vaccination campaign also may signal a change in the way in which vaccination programs are conducted in Africa.
Dr. Muhamed-Kheir Taha
"The concept of vaccination is changing in Africa," said Dr. Muhamed-Kheir Taha, director of the French National Reference Center for Meningococci at the Pasteur Institute in Paris, where he also is head of the invasive bacterial infections unit. "Previously, we had what we used to call ‘reactive vaccination,’ meaning we usually started vaccinating when the epidemiologic threshold was crossed, and now we are doing preventive vaccination."
In 2001, the World Health Organization (WHO) and the international nonprofit organization PATH founded the Meningitis Vaccine Project to develop MenAfriVac. The project brought together African ministers of health, U.S. government health agencies, philanthropic organizations, many strategic planning and surveillance groups, and vaccine industry partners.
MenAfriVac is being distributed to African nations in the meningitis belt, which stretches from Senegal to Ethiopia, before anywhere else. After Burkina Faso, the hyperendemic nations of Niger and Mali also began nationwide vaccination campaigns in December. If a funding gap of U.S.$475 million is met, the WHO expects that all 25 countries in the meningitis belt will be using the vaccine by 2015. If that happens, the reduction in the number of meningitis cases is expected to save U.S.$120 million annually in the period up to 2015 from national budgets that would be otherwise spent on costs for diagnosis and treatment, according to the WHO.
Photo credit: Courtesy WHO/R.Barry
A young woman in the district of Kaya in Burkina Faso receives a vaccination during the pilot phase of the MenAfriVac campaign in 2010.
The vaccination campaign began just before the start of the dry season (January to May) when the yearly epidemics occur. Major epidemics of the disease occur every 7-14 years, and in 2009 they infected more than 88,000 people and killed more than 5,000 across the region. Serogroup A Neisseria meningitidis causes 80%-85% of the epidemics, according to the WHO.
Epidemics of group A meningococcal disease have been impossible to stop with older polysaccharide vaccines, despite millions of doses that have been given to individuals during epidemics. These vaccines induce a systemic immune response that is independent of memory T-cell activation and lasts only 2-3 years. They are also poorly immunogenic in children younger than 2 years. Polysaccharide vaccines also do not reduce the carriage of N. meningitidis in the nasopharynx, the bacteria’s natural habitat, and thereby do not induce "herd immunity." This happens because polysaccharide vaccines induce only immunoglobulin M antibodies, which are not present on the surfaces of epithelial cells lining the nasopharynx, according to Dr. Taha.
In contrast, MenAfriVac is modeled after the successful group C conjugate polysaccharide vaccine first used in the United Kingdom in the late 1990s and early 2000s. Conjugate vaccines are built with a protein attached to the bacteria’s capsular polysaccharide antigen, which induces a longer-lasting T-cell dependent immune response. This response produces immunoglobulin G antibodies that are present on the surface of epithelial cells in the nasopharynx, reducing carriage of the bacteria and providing herd immunity. This means that children younger than 2 years can receive the vaccine. The antibodies formed with MenAfriVac will likely persist beyond 5 years, said Dr. Taha, who was not involved in the development of the vaccine.
Photo credit: Courtesy Serum Institute of India Ltd.
MenAfriVac is being distributed first to African nations in the meningitis belt, which stretches from Senegal to Ethiopia.
A single dose of MenAfriVac costs less than half a U.S. dollar, in part because it was developed for less than a tenth of the U.S.$500 million that conjugate vaccine development has typically cost. In comparison, Dr. Taha said, "the cost of the group C conjugate vaccine in Europe is about 30 euros, which is far away from [the price that] can be offered in Africa."
Clinical trials carried out in India and in several countries of the meningitis belt in people aged 1-29 years have shown that MenAfriVac is safe and has higher immunogenicity than the previous group A polysaccharide vaccine. In children aged 12-24 months, MenAfriVac induced 20-fold greater antibody levels than did the meningococcal A component of the licensed tetravalent ACWY polysaccharide vaccine. Ongoing trials are determining whether a single dose of the vaccine given to children aged 9-12 months will be sufficient to generate long-lasting protection (Vaccine 2009;27[Suppl. 2]:B13-19).