Has Wild Poliovirus Been Eliminated from Nigeria?

Michael Famulare,Amit Kapoor

doi:10.1371/journal.pone.0135765

Michael Famulare, Amit Kapoor

Open Access

https://doi.org/10.1371/journal.pone.0135765

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Journal: PloS one	Publication Date: Aug 28, 2015
Citations: 21	License type: CC BY 4.0

Affiliation: Institute for Disease Modeling, Bellevue Hospital Center

Abstract

Wild poliovirus type 3 (WPV3) has not been seen anywhere since the last case of WPV3-associated paralysis in Nigeria in November 2012. At the time of writing, the most recent case of wild poliovirus type 1 (WPV1) in Nigeria occurred in July 2014, and WPV1 has not been seen in Africa since a case in Somalia in August 2014. No cases associated with circulating vaccine-derived type 2 poliovirus (cVDPV2) have been detected in Nigeria since November 2014. Has WPV1 been eliminated from Africa? Has WPV3 been eradicated globally? Has Nigeria interrupted cVDPV2 transmission? These questions are difficult because polio surveillance is based on paralysis and paralysis only occurs in a small fraction of infections. This report provides estimates for the probabilities of poliovirus elimination in Nigeria given available data as of March 31, 2015. It is based on a model of disease transmission that is built from historical polio incidence rates and is designed to represent the uncertainties in transmission dynamics and poliovirus detection that are fundamental to interpreting long time periods without cases. The model estimates that, as of March 31, 2015, the probability of WPV1 elimination in Nigeria is 84%, and that if WPV1 has not been eliminated, a new case will be detected with 99% probability by the end of 2015. The probability of WPV3 elimination (and thus global eradication) is > 99%. However, it is unlikely that the ongoing transmission of cVDPV2 has been interrupted; the probability of cVDPV2 elimination rises to 83% if no new cases are detected by April 2016.

Highlights

Since the World Health Assembly announced the intention to eradicate polio worldwide in 1988, all countries except Pakistan, Afghanistan, and Nigeria have interrupted indigenous transmission of all three wild poliovirus (WPV) serotypes at least once [1]
For wild poliovirus type 1 (WPV1) and Wild poliovirus type 3 (WPV3), the green curves provide less conservative estimates based on the assumption that vaccination quality maintains mean Reff < 1 at the level estimated at the time of the last case
As of March 31, 2014, the model predicts that WPV3 has been eradicated globally and there is an 70% chance that Africa is completely wild-polio free for the first time in history

Summary

Introduction

Since the World Health Assembly announced the intention to eradicate polio worldwide in 1988, all countries except Pakistan, Afghanistan, and Nigeria have interrupted indigenous transmission of all three wild poliovirus (WPV) serotypes at least once [1]. Nigeria may be the country to achieve wild-type polio elimination. The most recent case of wild-type 1 (WPV1) in Nigeria occurred in July 2014 [2]. The most recent case of wild-type 3 (WPV3) seen globally occurred in Nigeria in November 2012 [1]. The last case of WPV1 in Africa occurred in Somalia at the tail end of the Horn of Africa Outbreak in August 2014.

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Conclusion