A case-control study has shown that 41 percent of meningitis occurred in children vaccinated against the disease. The vaccine's protective efficacy was minus 58 percent. This means that children are much more likely to get the disease if they are vaccinated. (J.A.M.A., 1988, Osterholm et al., 260: 1423-1428.) Jonas Salk, inventor of the IPV, testified before a Senate subcommittee that nearly all polio outbreaks since 1961 were caused by the oral polio vaccine.