The World Health Organization’s global polio eradication effort uses the live, attenuated poliovirus vaccines developed by Albert Sabin. When the eradication program was announced in 1988, the goal was to eliminate global poliomyelitis, then cease immunization with poliovirus at some point in the future. In 2002 an outbreak of polio in the Dominican Republic sent a warning that this goal might not be possible. Twenty-one cases of paralytic polio were caused by a vaccine-derived poliovirus strain (VDPV). Although it had been known since the 1960s that vaccine viruses excreted by vaccinees are neurovirulent revertants, their transmission potential was unknown.
The outbreak in the Dominican Republic, and several others that were subsequently identified, made it clear that VDPV strains posed a threat to the plan to cease polio immunization. In the worst case scenario, VDPV strains would continue to circulate after vaccination had stopped, endangering the growing number of non-immune individuals. Alan Dove and I suggested, in a 1997 Science article, that it might be prudent for WHO to switch to using the inactivated poliovirus vaccine, IPV, which cannot replicate in the recipient. Once OPV usage ended, the levels of circulating VDPVs would decrease until they no longer could trigger an outbreak. Careful monitoring of VDPV in sewage would indicate when it would be safe to stop immunization with IPV.
In early 2001 I spoke at a conference on disease eradication in Washington, DC, sponsored by the Institute of Medicine. The meeting was chaired by Joshua Lederberg, and attended by the directors of polio immunization programs from many countries. I gave a presentation in which I emphasized the need to switch from OPV to IPV to avoid the problem of circulating VDPVs. This proposal received a mixed response, but I recall in particular the comments of D.A. Henderson, the architect of smallpox eradication, who said:
So, we have then say 8 years or 7 years, whatever it is to gear up to the vaccine, then another 10 years in using the inactivated vaccine. This is just totally unrealistic. We are not going to have the financial support globally for this. There is no way it is going to come about and as an end-game strategy it is dreaming to believe that this is reasonable. So, it is just not on.
I was surprised at the decisiveness of his comments, but after all, someone who has eradicated smallpox is very sure of himself.
Now WHO has now come full circle, as discussed in the Science article cited below. They agree that a transition to IPV is needed, and are looking into new ways to produce and deliver the vaccine.
And D.A. Henderson also agrees that a switch to IPV is needed. I guess I wasn’t dreaming after all.
A. W. Dove (1997). The Polio Eradication Effort: Should Vaccine Eradication Be Next? Science, 277 (5327), 779-780 DOI: 10.1126/science.277.5327.779
L. Roberts (2009). POLIO ERADICATION: Rethinking the Polio Endgame Science, 323 (5915), 705-705 DOI: 10.1126/science.323.5915.705
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