LAGOS , Nigeria ( CNN ) -- More than 200 people have died of meningitis in the past week alone in Niger and Nigeria , according to the World Health Organization . A health care worker vaccinates a child during an earlier outbreak of meningitis in Niger . The disease is an epidemic in 76 areas of the two countries , the health agency reported Wednesday . A spokesman for W.H.O . in Nigeria , Dr. Olaokun Soyinka , said Saturday that the outbreak is bigger than usual and stretches across the African meningitis belt from east- to west-sub-Saharan Africa . The outbreak began around the start of the year , Soyinka told CNN . It usually peaks in the dry season because of dust , winds and cold nights , before dipping around May when the rains come , he said . A shortage of vaccines means officials are relying on `` effective prevention , '' in which they watch for outbreaks and then vaccinate people in the epicenter and surrounding areas , Soyinka told CNN . There have been nearly 25,000 suspected cases and more than 1,500 deaths in the meningitis belt in the first 11 weeks of the year , W.H.O . reported . More than 85 percent of those cases happened in northern Nigeria and Niger . Nigeria 's Ministry of Health has reported 17,462 suspected cases of meningococcal disease , including 960 deaths , the world health agency said . In the past week , it reported 4,164 suspected cases with 171 deaths . Sixty-six local government areas in Nigeria have crossed the epidemic threshold . Epidemic thresholds are a way the W.H.O . confirms the emergence of an epidemic so it can step up vaccinations and other management measures . Niger 's Ministry of Health has reported 4,513 suspected cases of meningococcal disease , including 169 deaths , since the start of the year . In the past week , 1,071 suspected cases and 30 deaths have been reported , the W.H.O . said . Ten of Niger 's 42 districts have crossed the epidemic threshold . By comparison , other countries are reporting fewer than 50 cases a week . Meningitis is an infection of the meninges , the thin lining that surrounds the brain and the spinal cord . Several different bacteria can cause meningitis but Neisseria meningitidis -- which is to blame for this outbreak -- is one of the most significant because of its potential to cause epidemics . Health authorities have released 2.3 million doses of vaccine to Nigeria and 1.9 million doses to Niger , the W.H.O . said . CNN 's Christian Purefoy in Lagos , Nigeria , contributed to this report .
W.H.O . The World Health Organization said it was working with the government of Guinea to investigate the outbreak. Outbreak stretches across African `` meningitis belt , '' at epidemic levels in 76 areas . Vaccine shortage forces an `` effective prevention '' approach . 25,000 suspected cases , 1,500 deaths in the belt in the first 11 weeks of 2009 .