Number Of Wild Poliovirus Cases Research Articles

Reported Polio cases in Pakistan during 2019

This report describes polio cases, vaccination uncertainty and challenges, and the way forward to eradicate polio from Pakistan. Numerous articles, government and non-government documents, and survey reports were studied and an online search was made to collect information on polio in Pakistan. Once again the polio vaccination program has been stopped and accused by the local community in Pakistan as a result an increase has been seen in polio cases in the last year. In 2019, a total of 117 wild poliovirus (WPV) and 18 circulating vaccine-derived poliovirus (cVDPV2) cases were reported from the country. The majority of cases were from the Khyber Pakhtunkhwa (KP) province as a result of polio vaccination uncertainty and many challenges faced by the vaccination program in the region. Pakistan reported their highest annual number of WPV cases as compared to last few years. This increase is not only an alarming threat for the country but also a key challenge for the global polio eradication movement. Increase awareness and raising immunization to over 100% in some areas especially in the remote area where every year many children missed vaccination to achieve global polio eradication goals.

Update on Vaccine-Derived Poliovirus Outbreaks - Worldwide, January 2018-June 2019.

Certification of global eradication of indigenous wild poliovirus type 2 occurred in 2015 and of type 3 in 2019. Since the launch of the Global Polio Eradication Initiative (GPEI) in 1988 and broad use of live, attenuated oral poliovirus vaccine (OPV), the number of wild poliovirus cases has declined >99.99% (1). Genetically divergent vaccine-derived poliovirus* (VDPV) strains can emerge during vaccine use and spread in underimmunized populations, becoming circulating VDPV (cVDPV) strains, and resulting in outbreaks of paralytic poliomyelitis.† In April 2016, all oral polio vaccination switched from trivalent OPV (tOPV; containing vaccine virus types 1, 2, and 3) to bivalent OPV (bOPV; containing types 1 and 3) (2). Monovalent type 2 OPV (mOPV2) is used in response campaigns to control type 2 cVDPV (cVDPV2) outbreaks. This report presents data on cVDPV outbreaks detected during January 2018-June 2019 (as of September 30, 2019). Compared with January 2017-June 2018 (3), the number of reported cVDPV outbreaks more than tripled, from nine to 29; 25 (86%) of the outbreaks were caused by cVDPV2. The increase in the number of outbreaks in 2019 resulted from VDPV2 both inside and outside of mOPV2 response areas. GPEI is planning future use of a novel type 2 OPV, stabilized to decrease the likelihood of reversion to neurovirulence. However, all countries must maintain high population immunity to decrease the risk for cVDPV emergence. Cessation of all OPV use after certification of polio eradication will eliminate the risk for VDPV emergence.

Achieving a polio free world

Recently, the World Health Organization (WHO) declared that the spread of polio is an international public health emergency, and a coordinated international response is sought. Although the importance of such a response is recognized, there are challenges to stopping the spread of polio and achieving a polio free world. The most important issue is directing limited national resources to the specific areas where polio is endemic. In an article published in BMC Medicine, Upfill-Brown and his colleagues recognized this problem and successfully identified the potential risk areas in Nigeria using a validated spatial predictive model of wild poliovirus circulation. They also showed that a lower vaccine-derived population immunity is associated with the probability of a higher number of wild poliovirus cases within a district. Identification of the potential risk areas and understanding the magnitude of risk may help direct limited resources of the endemic countries to areas most at risk to maximize the impact of interventions and motivate the people to participate in the intervention program. These efforts are crucial if these endemic countries hope to eradicate polio.Please see related research article: http://www.biomedcentral.com/1741-7015/12/92.

Predictive spatial risk model of polio virus to aid prioritization and hasten eradication in endemic countries

Background: Polio eradication was declared a “programmatic emergency for global public health” by the world health assembly in 2012. Efficient prioritization of high risk areas would greatly improve the impact of the substantial resources of the Global Polio Eradication Initiative. Currently, one method for polio risk assessment has been described in the litterature, however this method has not been historically validated and fails to address uncertainty. Methods & Materials: Data, including vaccination history, collected from individuals through Acute Flaccid Paralysis (AFP) surveillence in Nigeria and Pakistan, used to calculate district level immunity and relevant covariates. We constructed heirachical temporal bayesian models to reduce measurement error in data and spatially smoothed Poisson hurdle models to assess predictors of wild polio virus (WPV) tranmission. Best fitting models used to forecast future district infection, predictive accuracy assessed with reciever operating characteristic (ROC) analysis. Results: Measurement error models greatly reduce changes in indicators from one time period to another. Calculated population immunity is a strongly associated with the presence of WPV and number of WPV cases within a district in Nigeria. In Pakistan, routine immunization dose history (not available through Nigerian AFP data) and zero-dose fraction are strongly associated with both aspects of WPV tranmission. A district risk list ordered according to model outputs demonstrates high forecast accuracy historically, with mean area under the ROC curve greater than 0.80 over the past three years. Model uncertainty propogated through to rank uncertainty, and the probability of a district belonging in the highest risk N district list can be calcuated. Conclusion: The measurement error smoothing model is a useful tool for estimation of important variables at small adminsitrative areas. With the Poisson hurdle model, we can study differential relatitionships between predictors and two aspects of WPV tranmsission. Historically forecast accuracy confirms the usefulness of this modeling approach in a disease control and elimination application. The quantification of uncertainty is essential to inform objectives descisions regarding changes in prioritization status of a district from one time period to another. These models can be naturally extended to other vaccine-preventable diseases, such as measles. In Nigeria, these models have been incorporated into national program planning.

Polio Vaccination in Nigeria: The ?Good?, the ?Bad? and the ?Ugly?

With increase in the number of polio cases, Nigeria serves as the primary threat to a polio free world. The “good” the bad” and “the ugly” aspects of polio vaccination in Nigeria is discussed. In the ‘good’ aspect the number of wild poliovirus cases declined by over 90%, cVDPV 2 cases declined by 82%. Similarly, genetic clusters of both wild poliovirus type 1 and type 3 have reduced form 18 and 19 in 2009 to 2 respectively. The Immunity to polioviruses has improved in endemic States and new approaches for better identification of settlements and to promote community participation have been adopted in 2012. On the ‘bad ‘aspect, polio cases have increased from 21 in 2010 to 62 in 2011 and 84 in 2012 (7th September) with ongoing transmission of wild poliovirus type 1,3 and cVDPV2. Declined political oversight at critical juncture and non-Implementation of emergency plans in key infected areas has been observed. Non-compliance to the vaccine seems to be the major contributor to the increasing number of polio cases in the country. Lastly “the ugly” face focuses on the aftermath of the boycott of polio vaccination in northern States in 2003 amidst the rumor that the vaccine contained infertility drugs, causes poliomyelitis and spread HIV. After resolving the crisis, some parents in the north still resist compliance with the polio vaccination. Borrowing a leave from the rally organized by the polio victims, all Nigerians should complement the government efforts in ‘kicking’ polio out of the country.