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Zika Virus: History, Neurologic Disease, and Threat to the Americas
Hope for Zika Vaccine Stems from Precedent
Meningococcal Vaccine Showing Early Promise in Africa
Last December, the History of Vaccines blog covered the introduction of MenAfriVac (PsA-TT) to the African meningitis belt, an area stretching from Senegal to Ethiopia, where epidemic waves of meningitis occur and can last up to three years. In the largest of these epidemic waves in history, meningitis killed more than 25,000 people from 1996 to 1997.
Polysaccharide vaccines are sometimes used to try to control outbreaks after they have begun: so-called “emergency vaccination” efforts designed to keep meningococcal epidemics from spreading further. However, these types of reactive efforts are very expensive and difficult to manage, and polysaccharide vaccines do not induce long-lasting immunity against meningococcal bacteria. (For more about the different types of vaccines, see our article and Types of Vaccines activity.)
Within these African epidemics, between 80 and 85% of cases are caused by a single group of meningococcal bacteria: group A. In 2000, a group of global health leaders gathered together by the World Health Organization (WHO) determined that a meningitis vaccine could be developed specifically for use in Africa: a low-cost vaccine that would focus solely on the Group A bacteria. The Bill & Melinda Gates Foundation provided a ten-year grant for what would become the Meningitis Vaccine Project (MVP).
Over the next decade the MVP, a collaboration between WHO and PATH, led the long process of developing the conjugate meningococcal vaccine MenAfriVac, which was granted prequalification status by WHO on June 23, 2010. The final cost of the vaccine was just 40 cents per dose – a viable cost for widespread use in Africa – and starting six months ago, MenAfriVac was introduced in Burkina Faso, Mali, and Niger, with almost 20 million people aged 1 to 29 (the age range most at risk) being vaccinated. In Burkina Faso, nationwide vaccination coverage reached almost 100%.
This year, all three countries are reporting record lows in confirmed Group A meningitis cases during an epidemic season. No cases were reported in Mali, while Burkina Faso and Niger each reported four cases; all were unvaccinated. (In Burkina Faso, three of the four cases occurred in individuals from Togo, where the vaccine was not introduced.)
These encouraging initial reports are also accompanied by the results of two studies, just published in the New England Journal of Medicine, examining the immunogenicity (the ability of the vaccine to provoke an immune response) of MenAfriVac when compared to a polysaccharide vaccine. One of the studies also evaluated the ability of MenAfriVac to produce long-lasting immunity, which is not accomplished by polysaccharide vaccines without the use of many repeated boosters.
In the first study, 601 children aged 12 to 23 months randomly received either MenAfriVac, a polysaccharide meningococcal vaccine, or a control vaccine (against Haemophilus influenzae type b), with a randomly selected booster dose of MenAfriVac, the polysaccharide vaccine, or the control vaccine administered ten months later. In the second study, 900 subjects aged 2 to 29 years randomly received either MenAfriVac or the polysaccharide vaccine. Both studies were double-blinded, randomized, and controlled.
Both studies measured the activity of group A serum bacterial antibody, called SBA; SBA levels at four or more times higher than baseline have been used as evidence of protection against meningococcal disease, and to support licensing of conjugate vaccines against meningococcal disease in the United States.
In the first study, 96% of individuals receiving the MenAfriVac vaccine showed SBA levels at least four times as high as baseline; in the second, 78.2% of the individuals receiving MenAfriVac met this criteria. In both cases, these percentages were significantly higher than those achieved by the polysaccharide vaccine (and the SBA levels themselves were much higher), demonstrating that MenAfriVac generates an immune response against Group A meningococcal bacteria superior to that generated by the polysaccharide vaccine.
The first study also examined the ability of MenAfriVac to generate a long-lasting immune response. After 40 weeks, many more individuals who had received MenAfriVac demonstrated persistent antibody responses against Group A meningococcal bacteria than did those who had received the polysaccharide vaccine. These results suggest that the conjugate MenAfriVac vaccine may provide much longer-lasting protection against Group A-caused meningitis.
The results from both studies suggest that MenAfriVac has a similar safety profile to the polysaccharide vaccine, yet produces a stronger and longer-lasting immune response against Group A meningococcal bacteria, making it a superior choice for vaccination programs in the meningitis belt.
MenAfriVac is expected to be introduced to three more countries – Chad, Nigeria, and Cameroon – beginning this fall, while it’s hoped that widespread use of the vaccine will reach the entire meningitis belt by 2016. After initial mass vaccination programs, the Meningitis Vaccine Project hopes to eventually integrate the vaccine into existing immunization programs – and ultimately eliminate the most common cause of epidemic meningitis in Africa.
PATH has created a video showing the manufacture of the MenAfriVac vaccine at the Serum Institute of India. You can watch the full video below.
Sow SO, Okoko BJ, Diallo A, et al. Immunogenicity and Safety of a Meningococcal A Conjugate Vaccine in Africans. N Engl J Med 2011; 364:2293-2304. Available at:
Meningitis Vaccine Project
Meningitis Vaccine Project: Clinical trial PsA-TT-002 (the first study referred to in the NEJM paper):
Meningitis Vaccine Project: Clinical Trial PsA-TT-003 (the second study referred to in the NEJM paper):