RARE ADVERSE EVENTS ASSOCIATED WITH ORAL POLIOVIRUS VACCINE IN BRAZIL

Oral poliovirus vaccine (OPV) developed by A. Sabin has been effective ly used to control poliomyelitis in Brazil, and the last case with the isolation of a wild poliovirus strain occurred in March 1989. Althoug h the vaccine controlled the circulation of wild strains and poliomyel itis cases associated with these strains were not detected during the last eight years, rare cases classified as vaccine-associated paralyti c poliomyelitis (VAPP) have been detected. Molecular characterization studies of poliovirus strains isolated from VAPP cases and from health y contacts have confirmed that the isolates are derived from the Sabin vaccine strains and also detected genomic modifications known or susp ected to increase neurovirulence such as mutations and recombination. The molecular characterization of polioviruses isolated during the las t eight years from paralysis cases classified as Guillain-Barre (GBS) syndrome and transverse myelitits (TM), and from facial paralysis (FP) cases also confirmed the vaccine origin of the strains and demonstrat ed mutations known to increase neurovirulence. Analysis of the epidemi ologic data of these GBS, TM and FP cases demonstrated that in most of them the last OPV dose was given months or years before the onset of the disease and the isolation of the polioviruses. The temporal associ ation between the isolation of these strains and the GBS, TM and FP su ggested that the Sabin vaccine-derived poliovirus strains could also r arely trigger the diseases.