The bacterium neisseria meningitidis is responsible for annual outbreaks of meningitis that put millions at risk along Africa's "Meningitis belt." Six types of bacteria cause epidemics, but one dominates this region, known as strain A.
The disease infected a record 250,000 people -- and caused 25,000 deaths -- during an outbreak in 1996. Today, the introduction of a vaccine specific to this strain of bacteria has seen numbers fall, with less than 8500 cases reported as of 13 March 2016. Pictured, an immunization campaign in Niger,