Vaccine-associated paralytic poliomyelitis: a retrospective cohort study of acute flaccid paralyses in Brazil

Background At the present time, in Brazil and other countries in the Americ as, the only cases of paralytic poliomyelitis due to poliovirus are caused by vaccine strains. The recognition of possible determinants of vaccine-ass ociated paralytic poliomyelitis (VAPP) by public health surveillance and im munization programmes is relevant to inform the debate on criteria for case definition and vaccination strategies. Methods A retrospective cohort study based on the cases of acute flaccid pa ralysis (AFP) reported to the Ministry of Health (MoH) was designed, with t he objective of studying cases of VAPP in Brazil between 1989 and 1995. Cli nical, laboratory and epidemiological data from 3656 acute flaccid paralysi s (AFP) cases, 30 of them diagnosed as VAPP, were analysed. Results An 8.88 risk ratio of VAPP (95% CI:4.37-18.03) was found when compa ring individuals who received oral poliovirus vaccine (OPV) between 4 and 4 0 days before the onset of paralysis and individuals who did not receive th e vaccine within this period. A risk of 1 case/2.39 million first doses and 1 case/13.03 million OPV doses administered was estimated for the general population. Conclusions Cases of AFP who received OPV between 4 and 40 days before the onset of paralysis and had fever, a prodrome of gastrointestinal symptoms, history of first dose of OPV, isolation of vaccine poliovirus type 2, and y oung age deserve careful investigation, since they are at increased risk fo r the condition studied.