POLICY AND PRACTICE
I started to read the abstract to Jacob John's review on vaccine-associated paralytic polio (VAPP) in full agreement with his observation that wherever oral poliovirus vaccine (OPV) is used, there are risks of VAPP to vaccinees and their contacts. Indeed, where polio immunization programmes are poorly implemented, there are risks of circulating vaccine-derived polioviruses (cVDPV). However, by the time I reached the end of the abstract, I found myself seriously disagreeing with much of what Jacob John had to say, and even more so by the end of the article.
Jacob John raises the spectre of cVDPV to give credibility to the potential seriousness of revertent vaccine strains. We have known for many years that VAPP is a rare but measurable consequence of the use of OPV, and until relatively recently there had been no concern that outbreaks of polio followed VAPP cases. The greatest risks of cVDPV are when immunization coverage is low, but VAPP is more likely to occur the higher the coverage in any population.
I was seriously worried when I read the proposition that developing countries should shift to inactivated polio vaccine (IPV), and that once IPV coverage reached high levels, the withdrawal of OPV could begin. Did this mean that developing countries should introduce IPV as well as using OPV and discontinue the latter only when the IPV coverage was high? How would that impact on the costs of polio eradication? How would high IPV coverage be achieved? What does this say about inequalities when some children who will receive OPV are denied the benefits given to others, who receive IPV, within the same country? And how could a mixed programme be implemented in a developing country?
Many of Jacob John's arguments are based on the belief that many more doses of OPV are needed per child to protect against polio in developing countries than would be needed if IPV were used in the routine programme, and he advocates a switch to IPV to prevent the high cost of supplementary campaigns with OPV. This argument could be justified only if there was convincing evidence that IPV is as effective as or more effective than OPV in interrupting polio transmission in a developing country setting. Also, routine coverage would need to be sufficient to prevent the accumulation of enough children who are susceptible to polio and who might, therefore, sustain the transmission of wild polioviruses should they occur or even cVDPV should there be any OPV being used in the population. Given that the countries currently posing the final barriers to polio eradication are those with the lowest immunization coverage through routine services, this seems to be a high-risk approach. He suggests that primary immunization with diphtheriatetanuspertussis (DTP)-IPV plus a dose of DTP-IPV in the second year would be as effective as and safer than primary OPV immunization followed by annual doses in campaigns, until a child reached 5 years of age. Although this may be valid for individual protection, it brings high risks on a population basis, most especially in countries where routine primary coverage is low and routine fourth doses do not even exist.
It is true that many countries are switching to IPV, and it is also true that VAPP is as much a tragedy for the individual as the natural disease itself. Jacob John fails to identify how routine coverage can be brought up to levels at which IPV can be substituted for OPV, or even convinces that it needs to be used universally once polio transmission has been interrupted. In Cuba, where there is no routine provision of OPV outside of annual campaigns, cVDPV has not been documented in the face of excellent surveillance.
Finally, I was concerned by the statement that "developing countries ... should have been warned about VAPP". Polio eradication represents a phenomenal global partnership in health, between countries and international organizations. Nevertheless, there are responsibilities on all of the partners to be properly informed, especially those who accept responsibilities on behalf of their populations.
Conflicts of interest: none declared.