Data from one author suggesting a slight increase in the reversion of OPV to the wild-type genotype (at some bases of the virus) in children who receive OPV after previously receiving IPV are disputed by others as artifactual due to inappropriate comparison populations. It was suggested that reversion after an OPV only dose or following IPV-OPV should be the comparison point. Because there is a decrease in virus shedding in patients who previously received a dose of IPV, the overall net effect is uncertain.
All combinations of IPV and OPV are sufficiently immunogenic. A sequential IPV-OPV immunization schedule would probably prevent four to six of the cases of VAPP that occur in the United States annually. Two doses of IPV are required to prevent VAPP, and two doses of OPV are required for optimal mucosal immunity. The cost of a sequential IPV/OPV schedule would be higher than OPV only given current IPV pricing. A CDC-sponsored study showed that as demand for IPV increases and cost per dose of IPV decreases a break even point would be reached.
One schedule would be to give IPV at 2 and 4 months of age followed by two doses of OPV during the second year of life. By delaying OPV until the second year of life, it might be possible to prevent a few cases of VAPP from occurring in immunodeficient individuals. However, it could also delay the induction of adequate intestinal or mucosal immunity until the second year of life. This would be a problem only if wild-type poliovirus were introduced into the community. The first dose of OPV could be given at 6 months of age, with the second dose given at 15 months of age, but immunodeficient children could inadvertently be vaccinated. A three-dose IPV schedule during the first year of life followed by one or two doses of OPV in the second year of life could be used when combination vaccines become available. However, this would be slightly more expensive.
The option of allowing parents and providers to make an informed choice of which polio vaccine to administer to children was the next alternative presented. Three of the vaccine policy options that were discussed (OPV only,
The material in this section is adapted from a presentation by Neal Halsey and comments by other workshop speakers or participants.