CSU 3/2009: VACCINE DERIVED POLIOVIRUS
|Monday, 19th of January 2009|
1) ESTIMATING THE EXTENT OF VDPV
In this article from PLOS, Wringe and colleagues review the virological and epidemiological evidence on VDPV with special attention to case to infection ratios, paying particular attention to the large VDPV epidemics in Hispaniola, Indonesia and Egypt.
Wringe and colleagues do not minimize the importance of VDPV:
'To describe the problem of vaccine-derived polio as 114 virologically-confirmed cases, worldwide, over some twenty years, gives a very different impression than a description which suggests a minimum of hundreds of thousands, and more likely several million infections by vaccine-derived viruses, some of which became endemic in large populations. It is also possible that other vaccine-derived virus lineages have circulated for limited time periods, but failed to cause any clinical cases and were thus unrecognized. The risk of VDPV appearance and the incidence and spread of these infections will be important considerations for policies relating to the cessation of OPV, for future surveillance needs, and for planning for outbreak control in the future, including stockpiling vaccines.'
These findings have important implications for the future of polio vaccination policy. One solution to VDPV is stockpiling of monovalent OPV. But is the solution a problem if mOPV runs the risk of generating fresh VDPV? Can we eliminate the risk of VDPV without recourse to IPV?
2, 3) VDPV CASE REPORTS
4) WHAT WE DON'T KNOW ABOUT POLIO
Department of Microbiology and Neurology, School of Medicine, University of Pennsylvania, Philadelphia, PA
Wagner BG, Earn DJ, Bull Math Biol. 2008 Jan;70(1):253-80
Department of Mathematics and Statistics, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4K1, Canada. firstname.lastname@example.org
Poliomyelitis vaccination via live Oral Polio Vaccine (OPV) suffers from the inherent problem of reversion: the vaccine may, upon replication in the human gut, mutate back to virulence and transmissibility resulting in circulating vaccine derived polio viruses (cVDPVs). We formulate a general mathematical model to assess the impact of cVDPVs on prospects for polio eradication. We find that for OPV coverage levels below a certain threshold, cVDPVs have a small impact in comparison to the expected endemic level of the disease in the absence of reversion. Above this threshold, the model predicts a small but significant endemic level of the disease, even where standard models predict eradication. In light of this, we consider and analyze three alternative eradication strategies involving a transition from continuous OPV vaccination to either continuous Inactivated Polio Vaccine (IPV), pulsed OPV vaccination, or a one-time IPV pulse vaccination. Stochastic modeling shows continuous IPV vaccination is effective at achieving eradication for moderate coverage levels, while pulsed OPV is effective if higher coverage levels are maintained. The one-time pulse IPV method may also be a viable strategy, especially in terms of the number of vaccinations required and time to eradication, provided that a sufficiently large pulse is practically feasible. More investigation is needed regarding the frequency of revertant virus infection resulting directly from vaccination, the ability of IPV to induce gut immunity, and the potential role of spatial transmission dynamics in eradication efforts.