[Intense campaign for vaccination with the oral polio vaccine: what are the repercussions on the enterovirus world?].

To eradicate poliomyelitis and poliovirus, intensive vaccination campaigns with oral polio-vaccine (OPV) have been organised. Eradication campaigns may well be successful because the antiviral immunity and the local intestinal immunity due to OPV in particular avoids and/or limits poliovirus circulation. These campaigns give interesting opportunities for studying the impact of viral vaccines on the viral world in terms of ecological and genetic virology. The pre-eradication phase we are now entering brings with it two kinds of problems. First, the major disadvantage of OPV is the genetic and phenotypic variability of the vaccine strains. This variability leads to the spread of potentially pathogenic strains, which can be implicated in vaccine-associated paralytic poliomyelitis (VAPP). Genetic changes are characterised by point mutations and by genetic exchanges among OPV strains, between OPV and wild strains and perhaps between poliovirus and non-polio enteroviruses (ENPV). The fact that a few OPV mutant strains have been shown to multiply and/or to circulate for long periods suggests that OPV could sustain a reservoir of pathogenic poliovirus strains. Second, there are ecological considerations. The disappearance of wild poliovirus through OPV vaccination could be due not only to antiviral local immunity but also to competition between OPV strains and wild strains for infecting the digest tract. Moreover, a competition between OPV and other enteroviruses may take place in a common ecological niche. To our knowledge, the possible impact of intensive OPV vaccination campaigns on the ENPV populations has never been considered. Because the goal of poliovirus eradication may be reached in the near future, there is worry as to the possible evolution of ENPV towards highly epidemic and pathogenic strains. This is leading those laboratories involved in poliomyelitis surveillance not only to search for remaining wild poliovirus strains but also to study the possible long-term circulation of OPV strains and to develop efficient ENPV surveillance.