Background. After the 2001–2002 poliomyelitis outbreak due to recombinant vaccine-derived polioviruses
(VDPVs) in the Toliara province of Madagascar, another outbreak reoccurred in the same province in 2005.
Methods. We conducted epidemiological and virological investigations for each polio case patient and for their
contacts.
Results. From May to August 2005, a total of 5 cases of acute flaccid paralysis were reported among unvaccinated
or partially vaccinated children 2–3 years old. Type-3 or type-2 VDPV was isolated from case patients and from
healthy contacts. These strains were classified into 4 recombinant lineages that showed complex mosaic genomic
structures originating from different vaccine strain serotypes and probably from human enterovirus C (HEV-C)
species. Genetic relatedness could be observed among these 4 lineages. Vaccination coverage of the population was
very low (<50%).
Conclusions. The broad distribution of VDPVs in the province and their close genetic relationship indicate
intense and rapid cocirculation and coevolution of the vaccine strains and of their related HEV-C strains. The
occurrence of an outbreak due to VDPV ~3 years after a previous outbreak indicates that a short period with low
vaccination coverage is enough to create favorable conditions for the emergence of VDPV in this setting.
