The anterior discussion has not been taken up fully. Is the paralysis from a natural infection or a result from OPV? Suppose the child was infected with a wild strain at the time of administration of OPV. This could account for illness rather than a mutation in one of the Sabin serotypes. DNA sequencing may be required in order to find the pathogen that was actually involved. As wild strains are not a threat now, there is no reason to vaccinate. Another choice is to vaccinate with a killed virus. Nevertheless, the threat can be mutations and thus reversion to virulence.