Special Theme – Polio Eradication: End-Stage Challenges

Two obstacles — the laboratory containment of wild-type poliovirus and uncertainties about the threat posed by vaccine-derived poliovirus (VDPV) — still stand in the pathway towards the final eradication of poliovirus. Both issues have generated considerable controversy. Dowdle et al. have proposed a systematic and logical approach to the containment of wild-type poliovirus, which needs to be carefully considered (1). Isolated incidents of poliovirus escape from laboratories and inactivated polio vaccine (IPV) production facilities have been well documented (2–4). The consequences of such accidents could be far greater in a post-immunization world and cannot be ignored. The “roadmap” outlined by Dowdle et al. spells out three essential steps for containment — minimize the sites keeping the virus, minimize any operations that could pose a risk of spread, and minimize the susceptibility of workers who are potentially exposed to the virus. Undoubtedly, if effectively implemented, this would greatly reduce the risk of accidental spread. But will it be enough to assure future policy-makers when the final decision comes to stop vaccination? Much has been learnt from smallpox eradication and much wisdom can still be gleaned from that programme. However, laboratory containment was indeed simpler with smallpox and not entirely comparable to poliovirus. Biological materials contaminated with or containing wild-type poliovirus will be far more difficult to identify than in the case of smallpox, and live virus might well reside in specimens that are labelled and stored as something else (5). Unfortunately, there will be no short-cuts to the detailed laboratory documentation required for a comprehensive inventory of potential laboratory sources of virus — a task that will be particularly exacting with middle-income countries that have a combination of extensive laboratories, both inside and outside the virology field, and adequate freezer space, but perhaps inadequate record keeping. The potential weak link in Dowdle et al’s roadmap is its reliance for containment security on the commitment of a substantial number of laboratories that may wish to retain stocks and perhaps even work with live virus. The cessation of polio immunization must demand very special measures, even though absolute security and containment will never be achievable. First, the global regulation of laboratories needs to now be looked at with greater urgency, and poliovirus containment could well be the much-needed catalyst for this. This responsibility is probably best undertaken by WHO. Mechanisms will need to be implemented to enforce compliance, such as a requirement that reagent and material distribution be restricted to registered laboratories only. Second, eradicated infectious agents might well need a very special category of biohazard classification to justify the especially stringent laboratory regulations that were pioneered by smallpox eradication.