MenAfriVac meningitis vaccine an incredible success in Chad
A new meningitis vaccine, MenAfriVac or PsA-TT, has proved to be a raging success in after a mass vaccination campaign in the African country of Chad, according to new research published in The Lancet.
MenAfriVac, a conjugate polysaccharide-tetanus toxoid vaccine for type A meningitis, reduced the incidence of all cases of meningitis by 94 per cent in vaccinated regions.
The research team led by scientists from London School of Hygiene & Tropical Medicine and Centre de Support en Santé Internationale (CSSI) in Chad, evaluated the effectiveness of a mass vaccination campaign in Chad in 2011 by measuring the incidence of meningitis during the 2012 meningitis season and the number of people carrying the bacteria that cause the disease in their throat.
Approximately 1.8 million people aged 1-29 years received a single dose of PsA-TT (also known as MenAfriVac ®) in three regions of Chad in December 2011. The incidence of meningitis of any kind in these regions during the 2012 meningitis season was 2.5 per 100,000 people, compared to an incidence of 43.6 per 100,000 in regions where mass vaccination had not been undertaken – a difference of 94%. No cases of serogroup A meningococcal meningitis were detected in the three vaccinated regions.
The study’s author, Brian Greenwood of the London School of Hygiene and Tropical Medicine, described it as one of the most dramatic outcomes he had ever seen in a public health intervention.
In addition, carriage of the disease-causing bacteria was also dramatically reduced. Two to four months prior to vaccination, 32 serogroup A carriers were identified in 4,278 people tested through throat swabs. Four to six months following vaccination, only one out of 5,001 people tested in the same community was found to be carrying serogroup A.
The affordable PsA-TT vaccine was developed by the Meningitis Vaccine Project – a partnership between WHO and PATH – with funding from the Bill & Melinda Gates Foundation.
According to the World Health Organization, meningococcal meningitis is a bacterial form of meningitis, a serious infection of the meninges that affects the brain membrane. It can cause severe brain damage and is fatal in 50% of cases if untreated.
Several different bacteria can cause meningitis. Neisseria meningitidis is the one with the potential to cause large epidemics. Twelve serogroups of N. meningitidishave been identified, six of which (A, B, C, W135, X and Y) can cause epidemics. Geographic distribution and epidemic potential differ according to serogroup.
The meningitis belt of sub-Saharan Africa, stretching from Senegal in the west to Ethiopia in the east, has the highest rates of the disease. Chad is part of the so-called African meningitis belt.
Group A meningococcus accounts for an estimated 80–85% of all cases in the meningitis belt, with epidemics occurring at intervals of 7–14 years.
The bacterium, Neisseria meningitidis only infects humans; there is no animal reservoir. The bacteria can be carried in the throat and sometimes, for reasons not fully understood, can overwhelm the body’s defenses allowing infection to spread through the bloodstream to the brain. Although there remain gaps in our knowledge, it is believed that 10% to 20% of the population carries Neisseria meningitidis in their throat at any given time. However, the carriage rate may be higher in epidemic situations.
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