POLIOMYELITIS CASES DERIVED FROM THE ORAL POLIO VACCINE IN MADAGASCAR
Five cases of acute flaccid paralysis associated with strains of poliovirus derived from the oral polio vaccine (OPV) were registered in the south of Madagascar from October 2001 to April 2002. Researchers from the Institut Pasteurs in Paris and in Madagascar studied this strain at molecular level. The results have recently been published in Emerging Infectious Diseases : the study shows that the viral strains in question are recombining strains between vaccine strains and unidentified enterovirus strains. The emergence of these pathogenic viral strains derived from the vaccination complicates the eradication strategies for poliomyelitis.
Although no case of poliomyelitis due to wild poliovirus had been detected in Madagascar since 1997, these cases associated with poliovirus derived from the oral polio vaccine (OPV) make, according to researchers, the eradication of poliomyelitis more complex and mean that the planned stopping of vaccination with the OPV, the final stage of vaccination campaigns aiming to entirely destroy poliomyelitis and poliovirus, must be reconsidered.
The epidemic has affected the children of a southern province in the Republic of Madagascar, which had not been entirely vaccinated against poliomyelitis. Research teams of the Institut Pasteur in Paris and of the Institut Pasteur in Madagascar, respectively led by Francis Delpeyroux and Philippe Mauclère, have characterised the molecular structure of isolated viral strains. They have proved that they differ significantly from reference vaccine strains and, that they have probably evolved in recombination with other enteroviruses. vaccine strains may meet other types of enterovirus by circulating between different individuals and exchanging genetic material with these enteroviruses, thus leading to the emergence of new pathogenic viruses.
This was confirmed by the partial sequencing of a genome of the viral strains in question, which also led to the conclusion that these strains had multiplied or circulated for one to two and a half years, proving low vaccine coverage. These viral stains had "met" enough non-vaccinated individuals to multiply and circulate.
These cases occurred in a region where vaccine coverage against poliovirus was insufficient. High coverage allows the circulation of wild poliovirus and poliovirus derived from the vaccine to be prevented: this is therefore essential. In response to the epidemic, local health authorities have led a door to door vaccination campaign with the OPV, which has enabled the epidemic to be controlled. Ground research is underway to check whether the strains derived from the vaccine have spread, and to actively seek other potential cases.
This research demonstrates new aspects of the evolution of enteroviruses and highlights the need, from now on, to monitor not only the circulation of wild poliovirus in the world, but also that of viruses derived from vaccine viral strains.
Derived Poliovirus in Madagascar": Emerging Infectious Diseases
- July 2003, vol.9
Dominique Rousset (1), Mala Rakoto-Andrianarivelo (1), Richter Razafindratsimandresy (1), Bakolalalo Randriamanalina (2), Sophie Guillot (3), Jean Balanant (3), Philippe Mauclère (1) and Francis Delpeyroux (3)
1 Institut Pasteur in Madagascar,
Antananarivo, Republic of Madagascar
2 Health Ministry, Antananarivo, Republic of Madagascar
3 Institut Pasteur, Paris, France
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