Illustration of results from the stochastic dynamic mathematical model of VDPV2 emergence and spread.

<p>The model is simulated for 1 year and a population of 10,000 individuals, starting from a VDPV-free equilibrium that includes routine immunisation. OPV2 withdrawal occurs at 6 months (red arrow) and the last tOPV SIA is assumed to occur 4 weeks before this date in agreement with current plans. SIAs are implemented 4 weeks apart. We define the risk of a VDPV2 outbreak after OPV2 withdrawal as the probability of having >200 incident VDPV2 infections during the 6 months following OPV2 cessation. In this illustration, the grey lines represent the number of VDPV infected individuals over time for 20 different simulations of the model assuming 20% routine immunisation coverage and 3 tOPV SIAs with 80% coverage implemented before OPV2 withdrawal.</p

Univariable and multivariable analyses of cases (district−6-months where the first AFP case associated with a VDPV2 emergence was detected) vs. controls (district−6-months with no VDPV2 emergence).

<p>Abbreviations: CI, confidence interval; OR, odds ratio; <i>P</i>, p-value. Statistically significant p-values <0.05 are shown in boldface. Borderline significant p-values <0.1 are shown in italics.</p

Risk factors for an emergent VDPV2 to establish a circulating lineage associated with >1 case of poliomyelitis in Nigeria.

<p>Serotype-2 population immunity and DTP3 coverage in districts in the 6-month period when the first AFP case associated with each of the 29 independent VDPV2 emergences in Nigeria during 2004−2014 were reported. Red triangles represent isolates that established circulating lineages, whereas blue circles represent single isolates.</p

Early childhood education Perceptions, problems and possibilities

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Risk factors associated with the incidence of wild poliovirus type 1 (WPV1) cases based on the best-fitting multivariable mixed-effects lagged regression model for January–June 2010 through July–December 2016.

<p>The odds ratio (OR) and the 95% confidence interval (CI) for routine immunization and supplementary immunization activity (SIA) coverage are for an absolute 10% increase in these variables and a 1-unit increase for all other variables. Non-polio acute flaccid paralysis (AFP) rate is per 100,000 persons aged <15 years.</p

Spatio-temporal correlation between serotype-2 population immunity and the occurrence of cVDPV2 cases.

<p>Country estimates of serotype-2 population immunity and monthly number of cases of cVDPV2 in (A) Nigeria and (B) Pakistan. Proportion of districts (with 95% confidence intervals) reporting at least one cVDPV2 case within a 6-mo period among all districts/6-mo periods by intervals of 10% of estimated serotype-2 population immunity for (C) Nigeria and (D) Pakistan.</p

Reported and model-based estimates and forecasts of wild poliovirus type 1 (WPV1) cases between July 2013 and December 2016.

<p>(A) Observed WPV1 cases. (B) Estimated probability of reporting at least 1 WPV1 case based on the best-fit regression model including all available data (January 2010–December 2016). Complete figures with earlier time periods included in Figures K and L in <a href="http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.1002323#pmed.1002323.s002" target="_blank">S1 Text</a>. (C) Predicted probability of reporting at least 1 WPV1 case for the same periods using data up to the end of the preceding 6-month period. AUC, area under the curve.</p

Illustration of the estimated force of infection (FOI) resulting from the movement of infected individuals between districts during January to June 2014.

<p>In (A), the components of the FOI are shown. Wild poliovirus type 1 (WPV1) cases in the previous 6 months (shown on the left) and estimated population movement calculated from the radiation model (shown for movement out of 2 chosen districts, centre, highlighted in dark blue) result in a district-specific FOI (right). The interplay between the FOI and the susceptibility of the population (population immunity, B) to determine the incidence of WPV1 cases in that 6-month period (C).</p

Estimated serotype-2 population immunity in January–June 2015 and projected serotype-2 population immunity in April 2016 in Nigeria and Pakistan.

<p>Estimated serotype-2 population immunity in January–June 2015 in (A) Nigeria and (C) Pakistan. Projected serotype-2 population immunity at the moment of OPV2 withdrawal (April 2016) in (B) Nigeria and (D) Pakistan. The inserts of (C) and (D) show the administrative areas of Karachi. The publication of this map does not imply the expression of any opinion whatsoever on the part of WHO concerning the legal status of any territory, city, or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.</p

Spatial distribution and trends in the incidence of poliomyelitis over time in different regions of Pakistan.

<p>In (A), the spatial distribution of wild poliovirus type 1 (WPV1)-associated poliomyelitis cases in districts of Pakistan between January 2010 and December 2016 is shown (red dots). (B) Monthly confirmed WPV1-associated poliomyelitis cases in Pakistan reported between January 2010 and December 2016 are shown (bars). The same data are shown together with estimated serotype 1 vaccine-induced population immunity among children <36 months old (lines) for (C) Punjab, Sindh, Islamabad, Azad Jammu and Kashmir (AJK), and Gilgit-Baltistan, (D) Khyber Pakhtunkhwa, (E) Balochistan, and (F) the Federally Administered Tribal Area (FATA).</p