Provocation of poliomyelitis by multiple injections.

Injections of vaccines provoked paralytic poliomyelitis in children in the UK and elsewhere. The effect of multiple injections has not been recognized previously but could be important in the tropics where children receive many injections. A number of epidemics of poliomyelitis between 1914 and 1962 are related to children with congenital syphilis or yaws under treatment with arsenicals or penicillin. Rates of 25% of children with paralysis occurred in epidemics while in non-epidemic periods the increase in susceptibility was about 25 fold. Other possible cases of provocation are discussed. Although in the tropics injections before paralysis may be causal, it will be difficult to prove that they are not coincident. The very high rate of paralysis following multiple injections is powerful evidence that injections in the tropics are often causal.