Apparent global interruption of wild poliovirus type 2 transmission

In 1988, the World Health Assembly of the World Health Organization (WHO) resolved to eradicate poliomyelitis by 2000. Since then, the WHO Region of the Americas and Western Pacific Region have been certified free of polio, and the European Region is approaching 3 years since the last confirmed case of polio. Transmission of wild poliovirus types 1 and 3 continues to decline in the other WHO regions. This report summarizes the evidence, obtained through surveillance for acute flaccid paralysis (AFP), supporting the global interruption of wild poliovirus type 2 transmission.     

The probability of undetected wild poliovirus circulation after apparent global interruption of transmission

The Global Polio Laboratory Network maintains active surveillance for circulating live polioviruses by obtaining and testing stool samples from patients with acute flaccid paralysis. However, most poliovirus infections occur with no symptoms, and questions remain about the probability of undetected wild poliovirus (WPV) circulation after the apparent interruption of WPV transmission in different populations. In the context of making decisions about the timing of oral poliovirus vaccine cessation following global eradication of WPV, policy-makers need an understanding of this probability as a function of time. Prior modeling of the probability of undetected circulation relied on relatively simple models and assumptions, which limits extrapolation to current conditions. In this analysis, the authors revisit the topic and highlight important considerations for policy-makers related to the impact of initial conditions and seasonality and emphasize the need to focus on appropriate characterization of conditions in the last likely reservoirs of the virus. The authors conclude that the probability of undetected WPV circulation may vary significantly for different poliovirus serotypes, places, and conditions, which suggests that achieving the same level of confidence about the true interruption of WPV transmission will require different periods of time for different situations.     

Poliovirus seroprevalence before and after interruption of poliovirus transmission in Kano State,Nigeria

IntroductionIn September 2015, Nigeria was removed from the list of polio-endemic countries after more than 12 months had passed since the detection of last wild poliovirus case in the country on 24 July 2014. We are presenting here a report of two polio seroprevalence surveys conducted in September 2013 and October 2014, respectively, in the Kano state of northern Nigeria.MethodsHealth facility based seroprevalence surveys were undertaken at Murtala Mohammad Specialist Hospital, Kano. Parents or guardians of children aged 6–9 months, 36–47 months, 5–9 years and 10–14 years in 2013 and 6–9 months and 19–22 months (corresponding to 6–9 months range at the time of 2013 survey) in 2014 presenting to the outpatient department, were approached for participation, screened for eligibility and asked to provide informed consent. A questionnaire was administered and a blood sample collected for polio neutralization assay.ResultsAmong subjects aged 6–9 months in the 2013 survey, seroprevalence was 58% (95% confidence interval [CI] 51–66%) to poliovirus type 1, 42% (95% CI 34–50%) to poliovirus type 2, and 52% (95% CI 44–60%) to poliovirus type 3. Among children 36–47 months and older, seroprevalence was 85% or higher for all three serotypes. In 2014, seroprevalence in 6–9 month infants was 72% (95% CI 65–79%) for type 1, 59% (95% CI 52–66%) for type 2, and 65% (95% CI 57–72%) for type 3 and in 19–22 months, 80% (95% CI 74–85%), 57% (49–63%) and 78% (71–83%) respectively. Seroprevalence was positively associated with history of increasing oral poliovirus vaccine doses.ConclusionsThere was significant improvement in seroprevalence in 2014 over the 2013 levels indicating a positive impact of recent programmatic interventions. However the continued low seroprevalence in 6–9 month age is a concern and calls for improved immunization efforts to sustain the polio-free Nigeria.     

Progress toward interruption of wild poliovirus transmission--worldwide, January 2004-March 2005

In 1988, the World Health Assembly of the World Health Organization (WHO) resolved to eradicate poliomyelitis globally. Since then, substantial worldwide progress has been made toward that goal; the number of countries where polio is endemic declined from 125 in 1988 to six by the end of 2003. Further progress in 2004 toward interruption of transmission has continued in the three Asian countries where polio is endemic (Afghanistan, India, and Pakistan). However, in 2003, two countries in Africa experienced a resurgence of polio cases; the resurgence continued to spread in 2004 from the Nigeria-Niger endemic reservoir to involve a total of 14 countries that had not reported polio > or =1 year. Local transmission of wild poliovirus (WPV) has been reestablished in six of these 14 countries, including Sudan, where a major outbreak occurred. This report describes global efforts to eradicate polio during January 2004-March 2005 and outlines remaining challenges to interrupting transmission in countries where polio remains endemic or transmission has been reestablished.     

Progress toward interruption of wild poliovirus transmission--worldwide, January 2006-May 2007

Progress toward global polio eradication continued during 2006 and the first 5 months of 2007, although the number of countries where wild poliovirus (WPV) transmission has never been interrupted remained at four (Afghanistan, India, Nigeria, and Pakistan). Continuing challenges included intense WPV circulation in northern India during 2006, low vaccination coverage with oral polio vaccine (OPV) during supplemental immunization activities (SIAs) in Nigeria, and security problems preventing access to children during SIAs along the Afghanistan-Pakistan border. Programmatic strategies to address these challenges consisted of large-scale use of type 1 monovalent oral polio vaccine (mOPV1), targeted programs (e.g., cross-border synchronization of polio campaigns) to reach more children through SIAs, and introduction of new laboratory procedures to confirm cases more rapidly. This report summarizes these strategies and overall progress toward global polio eradication.     

Progress toward interruption of wild poliovirus transmission--worldwide, January 2011-March 2012

In January 2012, completion of polio eradication was declared a programmatic emergency for global public health by the Executive Board of the World Health Organization (WHO). Despite major progress since the launch of the Global Polio Eradication Initiative (GPEI) in 1988, circulation of indigenous wild poliovirus (WPV) continues in three countries (Afghanistan, Nigeria, and Pakistan). India has not reported a polio case since January 2011, and is considered polio-free since February 2012. This report highlights progress toward global polio eradication during January 2011-March 2012. The number of polio cases reported globally decreased by 52%, from 1,352 in 2010 to 650 in 2011. Those 650 cases included 341 (53%) reported from the four polio-endemic countries (Afghanistan, India, Nigeria, and Pakistan), 230 (35%) from previously polio-free countries in which WPV importations led to reestablished transmission for ≥12 months (Angola, Chad, and Democratic Republic of the Congo [DRC]), and 79 (12%) from nine countries affected by outbreaks. Compared with 2010, WPV cases increased in 2011 in Afghanistan (69%), Nigeria (66%), and Pakistan (27%), but decreased in India (98%). During January-March 2012, 59% fewer cases were reported worldwide (as of May 15) compared with the same period in 2011, and all cases in 2012 have been reported from Afghanistan, Chad, Nigeria, and Pakistan. Although progress toward polio eradication was substantial in 2011, persistent WPV circulation in 2012, particularly in Nigeria and Pakistan, poses an ongoing threat to eradication efforts, underscoring the need for emergency measures by polio-affected countries and those at risk for outbreaks after importation.     

Progress toward interruption of wild poliovirus transmission--worldwide, January 2007-April 2008

In 1988, the World Health Assembly resolved to eradicate poliomyelitis. Subsequently, the Global Polio Eradication Initiative reduced the global incidence of polio associated with wild polioviruses (WPVs) from an estimated 350,000 cases in 1988 to 1,997 reported cases in 2006 and reduced the number of countries that have never succeeded in interrupting WPV transmission from 125 to four (Afghanistan, India, Nigeria, and Pakistan). Type 2 WPV (WPV2) circulation was last observed in October 1999. In February 2007, the World Health Organization (WHO) convened a stakeholders meeting to agree on an accelerated polio-eradication effort to be used during 2007-2008 and establish milestones to monitor progress. Programmatic strategies implemented in 2007 included expanded use of type 1 monovalent oral poliovirus vaccine (OPV) (mOPV1) to eliminate type 1 WPV (WPV1) transmission before type 3 WPV (WPV3) and targeted use of type 3 monovalent OPV (mOPV3) in selected areas. This report summarizes these strategies and overall progress toward reaching the milestones, including a decline in the overall number of WPV cases to 1,310 in 2007 and substantial progress toward interruption of WPV1 circulation in India in 2008.     

Progress toward interruption of wild poliovirus transmission--worldwide, January 2010-March 2011

The Global Polio Eradication Initiative (GPEI) was launched in 1988. By 2006, transmission of indigenous wild poliovirus (WPV) was interrupted in all but four countries (Afghanistan, Pakistan, India, and Nigeria). Subsequently, 39 previously polio-free countries experienced outbreaks following importation of WPV, and transmission became reestablished in Angola, Chad, Democratic Republic of the Congo (DRC), and Sudan. This update summarizes progress toward polio eradication during 2010 and the first quarter of 2011. Worldwide, 1,291 WPV cases were reported in 2010, a 19% decrease from 2009; WPV type 3 (WPV3) cases decreased 92%, but WPV type 1 (WPV1) cases increased 145%. During 2010, 232 (18%) WPV cases were reported from the four polio-endemic countries; 159 (12%) cases were reported in Angola, Chad, and DRC; and 900 (70%) cases were reported in 13 countries, including two countries with outbreaks continuing from 2009 and 11 with new importations. During 2010, WPV cases in India and Nigeria decreased ≥94% compared with 2009. Outbreaks in Tajikistan and the Republic of the Congo (Congo) accounted for two thirds of cases (842) in 2010. All new outbreaks in 11 polio-free countries in 2010 were stopped or were on track to being stopped within 6 months of outbreak confirmation. During January--March 2011, substantially more WPV cases occurred in Chad, DRC, and Pakistan than during the same period of 2010. To further progress toward polio eradication and achieve the 2012 target of ending all WPV transmission, significant increases in resources and political commitment are needed.     

Progress toward interruption of wild poliovirus transmission--worldwide, January 2005-March 2006

Progress toward global poliomyelitis eradication was made in 2005, despite the diversion of major financial and human resources to control outbreaks resulting from wild poliovirus (WPV) importations primarily from Nigeria. The number of countries with endemic polio has decreased to four, compared with 125 in 1988, when the Polio Eradication Initiative was initiated by the World Health Assembly . In Africa and Asia, only eight of the 22 previously polio-free countries that were reinfected since 2003 reported WPV transmission after July 2005, and transmission was curtailed substantially in all eight of these countries except Somalia. Of the three remaining polio-endemic countries in Asia (Afghanistan, India, and Pakistan), India and Pakistan also moved closer to eradication in 2005, reporting approximately half as many cases in 2005, compared with 2004.     

Massive outbreak of poliomyelitis caused by type-3 wild poliovirus in Angola in 1999

The largest outbreak of poliomyelitis ever recorded in Africa (1093 cases) occurred from 1 March to 28 May 1999 in Luanda, Angola, and in surrounding areas. The outbreak was caused primarily by a type-3 wild poliovirus, although type-1 wild poliovirus was circulating in the outbreak area at the same time. Infected individuals ranged in age from 2 months to 22 years; 788 individuals (72%) were younger than 3 years. Of the 590 individuals whose vaccination status was known, 23% had received no vaccine and 54% had received fewer than three doses of oral poliovirus vaccine (OPV). The major factors that contributed to this outbreak were as follows: massive displacement of unvaccinated persons to urban settings; low routine OPV coverage; inaccessible populations during the previous three national immunization days (NIDs); and inadequate sanitation. This outbreak indicates the urgent need to improve accessibility to all children during NIDs and the dramatic impact that war can have by displacing persons and impeding access to routine immunizations. The period immediately after an outbreak provides an enhanced opportunity to eradicate poliomyelitis. If continuous access in all districts for acute flaccid paralysis surveillance and supplemental immunizations cannot be assured, the current war in Angola may threaten global poliomyelitis eradication.     

Perspectives on rapid elimination and ultimate global eradication of paralytic poliomyelitis caused by polioviruses

Poliomyelitis caused by polioviruses has already been eradicated from industrialized countries of North America, Europe, Asia and Oceania, but the procedures by which this eradication was achieved are not adequate for the poor tropical and subtropical countries. The major challenge now is first to eliminate it rapidly from Asia and Africa where an estimated 250,000 cases and 25,000 deaths currently occur annually. The great progress toward eradication of wild polioviruses from poor tropical and subtropical countries in Latin America was achieved not by the procedures still recommended by the WHO Expanded Program on Immunization (EPI) but by the independently organized annual, national days of antipolio vaccination — all based on the use of large armies of well-trained non-professional, community volunteers — first used in Cuba (1962), Brazil (1980), Nicaragua (1981), Dominican Republic (1983), Paraguay (1985), and Mexico (1986). This novel approach, described in some detail in this communication, is recommended for the rapid elimination of wild polioviruses from Asia and Africa, and for ultimate global eradication with the help of a special cadre within the EPI of WHO. The extensive use by the Pan American Health Organization (PAHO) of highly sophisticated regional virus laboratories has led to the recognition that, in areas from which poliomyelitis caused by polioviruses has been largely eliminated, there are thousands of cases of acute flaccid paralysis, previously clinically diagnosed as probable poliomyelitis, that have no viral etiology, a phenomenon previously reported by Dr. Manuel Ramos Alvarez in Mexico City in 1967.     

Immunogenicity of oral poliomyelitis vaccine (OPV) against variants of wild poliovirus type 3

Serological investigations of three groups of children from the German Democratic Republic (GDR) and from Czechoslovakia who had different immunization histories against poliomyelitis indicated that the immunity induced by oral poliovaccine (OPV) is effective against both the wild poliovirus Saukett strain and a new wild variant of poliovirus type 3 that was isolated during an outbreak of poliomyelitis in Finland in 1984. There is therefore no obvious risk that individuals in the GDR or Czechoslovakia, most of whom have been immunized with OPV, are threatened by new wild poliovirus variants. These findings are of importance, especially in connection with WHO's initiative for the global eradication of poliomyelitis by the year 2000.     

Seroimmunity to poliomyelitis in Sweden after the use of inactivated poliovirus vaccine for 10 years

This study was undertaken in 1968 in collaboration with the World Health Organization as part of a co-operative evaluation of vaccination programmes. The situation in Sweden was of particular interest as only inactivated vaccines had been used for immunization against poliomyelitis. The WHO programme includes evaluation of both seroimmunity and resistance to poliovirus infection but the present report concerns only the serological studies.     

The case for global eradication of poliomyelitis

Global eradication of poliomyelitis can be achieved by a programme strategy that includes achievement and maintenance of high immunization levels, effective surveillance to detect all new cases, and a rapid vigorous response to the occurrence of new cases. Regional eradication targets have already been set in Europe and the Americas. Possible impediments to eradication include the necessity to generate political and social will; managerial constraints; issues of vaccine efficacy, stability, and cost; and adequacy of surveillance. We believe that the impediments can be overcome and that with intensified effort and increased international collaboration, global eradication could be achieved as early as 1995.     

The logic of causation and the risk of paralytic poliomyelitis for an American child

Beginning in January 1997, American immunization policy allowed parents and physicians to elect one of three approved infant vaccination strategies for preventing poliomyelitis. Although the three strategies likely have different outcomes with respect to prevention of paralytic poliomyelitis, the extreme rarity of the disease in the USA prevents any controlled comparison. In this paper, a formal inferential logic, originally described by Donald Rubin, is applied to the vaccination problem. Assumptions and indirect evidence are used to overcome the inability to observe the same subjects under varying conditions to allow the inference of causality from non-randomized observations. Using available epidemiologic information and explicit assumptions, it is possible to project the risk of paralytic polio for infants immunized with oral polio vaccine (1.3 cases per million vaccinees), inactivated polio vaccine (0.54 cases per million vaccinees), or a sequential schedule (0.54-0.92 cases per million vaccinees).     

Comparison of methods for estimating the frequency of paralytic poliomyelitis in developing countries.

Standard reporting systems have proved to be unreliable in estimating the frequency of paralytic poliomyelitis in many developing countries. The effectiveness of three survey methods for estimating the prevalence of lameness attributable to poliomyelitis were compared in the Danfa Health Project district of rural Ghana. Lameness was studied because it is easily identified by inexpensive survey techniques. A postal survey of school headteachers was the least costly and most accurate method, giving a prevalence of lameness attributable to poliomyelitis of 7.2 per 1000 schoolchildren. This method is recommended for countries with an extensive network of primary schools. Medical examinations in a village health survey yielded a prevalence of 4.6 per 1000 children aged 6-15 years. This method was relatively expensive but could be justified if the survey was multipurpose. A question added to the annual district census showed a prevalence of 2.2 per 1000 children, a rate still many times higher than estimates from national statistics. The inclusion of such a question in a census or other national survey entails little additional cost and with more careful questioning results should improve. Repeated surveys can be used to assess the success of poliomyelitis vaccination programmes.