Cases Of Poliomyelitis Research Articles

The value of ProMED-mail for the Early Warning Committee in the Netherlands: more specific approach recommended

This article describes a retrospective and descriptive study into the added value of ProMED-mail--the global electronic reporting system for outbreaks of emerging infectious diseases and toxins maintained by the International Society for Infectious Diseases--as an early warning system for The Netherlands Early Warning Committee (NEWC). Information about infectious disease events in foreign countries originating from ProMED-mail was retrieved from the reports of the NEWC between May 2006 and June 2007. Each event was analysed in depth in order to determine if it could have been a possible threat to public health in The Netherlands. It was determined whether these events were mentioned in other sources of information used by the NEWC besides ProMED-mail. In addition, we assessed the possible consequences of missing an event when not reading ProMED-mail or of being informed of the event with a time delay. Semi-structured interviews with stakeholders were conducted to explore other functions of ProMED-mail besides early warning. Five out of 25 events reported in ProMED-mail were assessed as a potential threat to The Netherlands, mainly because of the known vulnerability of The Netherlands for vaccine preventable diseases: an outbreak of measles in the United Kingdom and Japan, a case of poliomyelitis in Kenya, and two events concerning Highly Pathogenic Avian Influenza (HPAI) H5N1. The outbreak of measles in Japan and one case of HPAI H5N1 infection in a bird in Germany were only reported by ProMED-mail; the other potential threats were mentioned in other sources with a time delay. ProMED-mail has a limited but real added value over other sources in the early warning of threats. A more specific approach of using ProMED-mail by defining vulnerabilities of a country would be useful and efficient. ProMED-mail is appreciated for providing background and preliminary outbreak information.

Letters to the Editor

1 March 2007 Dear Editor, POLIOMYELITIS – ACUTE FLACCID PARALYSIS AND STOOL VIROLOGY I write on behalf of the Poliomyelitis Expert Committee of the Commonwealth Department of Health and Ageing, to stress the importance of submitting stool specimens for virological analysis, in cases of acute flaccid paralysis (AFP), and particularly in those cases where poliomyelitis, however, unlikely, must be included in the differential diagnosis. The last case of wild-type poliomyelitis occurred in Australia in the early 1970s, and the last case of vaccine-associated poliomyelitis occurred in 1996. Since that time, Australia has been poliomyelitis-free. Nevertheless, every year there have been cluster outbreaks of poliomyelitis in countries that Australians visit and from which Australians return. The 2005/6 outbreak of clinical poliomyelitis in Indonesia was of significant concern to all monitoring bodies. Currently, almost three million Australians travel overseas each year and almost six million overseas visitors come here. The current immunisation-completion rate for poliomyelitis, for Australians, is 86% after the age of 6 years. There is obviously great need for meticulous surveillance, early diagnosis in the event of any clinical case occurring in Australia, and continued promotion of immunisation. The poliomyelitis virus remains viable and potentially infectious outside the body for some 8 weeks in faecal-contaminated soil or water. If poliomyelitis were reintroduced into Australia, the personal, logistic and administrative costs of eradication would be great, and have huge repercussions. Such would be further exacerbated by delayed diagnosis. The national Poliomyelitis Expert Committee, a committee of the Commonwealth Department of Health and Ageing, functions executively from the Victorian Infectious Diseases Reference Laboratory based in Melbourne. The Poliomyelitis Expert Committee monitors every case of AFP reported to it from multiple sources of case finding, principally through reports from the Australian Paediatric Surveillance Unit. Approximately 70 cases of AFP are reviewed in detail each year with final diagnoses ranging from Guillaine–Barré syndrome to tick paralysis. The ‘gold standard’, by which children with various forms of paralysis can be certified not to have poliomyelitis, is by negative culture of two stool-specimens submitted for virological culture, collected 24 h apart and within 14 days of onset of paralysis. Currently, the rate of submission of such stool specimens is only 16%. It is essential, in any newly presenting child with AFP, in which acute poliomyelitis or other neurotropic viruses must be considered in the differential diagnosis, to have such stool specimens submitted for culturing. This is done through one’s own local hospital pathology laboratory, to be forwarded to the National Polio Reference Laboratory located at the Victorian Infectious Diseases Reference Laboratory, 10 Wreckyn Street, North Melbourne, Victoria 3051, Australia (Tel: 03 9342 2600; Fax: 03 9342 2665; email: polio@mh.org.au). In the context of the ongoing ever-present risk of a poliomyelitis case occurring in Australia, may I join with many colleagues in promoting the strongest advocacy for the submission of stool specimens for virological analysis in all non-traumatic patients with AFP.

Characterization of mutations in the VP 1 region of Sabin strain type 1 polioviruses isolated from vaccine-associated paralytic poliomyelitis cases in Iran

Background The live-attenuated oral polio vaccine used to interrupt poliovirus transmission is genetically unstable. Reversion of some attenuating mutations, which normally occurs during vaccine strain replication in some recipients, and can rarely cause vaccine-associated paralytic poliomyelitis (VAPP). The poliovirus eradication program designed by the World Health Organization (WHO) includes immunization with OPV in addition to careful surveillance of all acute-flaccid paralysis (AFP) cases. Objectives In Iran we last isolated imported wild poliovirus in 2000 and the immunization coverage was 100% in 2002. During 2001, there were three AFP cases with residual paralysis from which Sabin-like type 1 polioviruses were isolated in our national polio laboratory. Study design The complete VP 1 region of the three isolates was sequenced and amino acid substitutions associated with these neurovirulent isolates were recorded. Results These isolates had either 4, 2 or 1 nucleotide substitution(s) in the VP 1 region, corresponding to amino acid change in the VP 1 of isolate 1 of either ( H ⟶ 149 Y ), ( T ⟶ 106 A ) or ( I ⟶ 90 L ), respectively. Conclusions Surveillance of the VAPP cases in countries where endemic transmission has recently ceased increases our understanding of the important neurovirulent mutations in vaccine-strain isolates and assists in planning the next step in the eradication program in these countries.

Seroprevalence of antibodies to poliovirus in individuals living in Portugal, 2002

The last case of poliomyelitis in Portugal caused by indigenous wild poliovirus occurred in 1986 and the country was declared polio-free in 2002. High levels of immunity must be maintained to prevent the importation of wild poliovirus. In this study, we determined the immunity against poliomyelitis of the Portuguese population in order to identify possible immunity gaps. A representative sample of 1,133 individuals older than two years residing in mainland Portugal was studied. Logistical difficulties regarding quick sample transportation precluded the Portuguese islands (Madeira and the Azores) from this study. Sera were collected in 2002 from individuals attending health clinics throughout the 18 districts of Portugal. Levels of neutralizing antibodies against poliovirus types 1, 2 and 3 were determined and a titre of > or = 1:8 was defined as indicative of protected immunity. Results were expressed in international units. The antibody prevalence and the geometric mean antibody concentration (GMAC) was 91.6% (GMAC: 2.96 IU/ml), 94.2% (GMAC: 5.03 IU/ml) and 75% (GMAC: 0.53 IU/ml) for poliovirus types 1, 2 and 3, respectively. For poliovirus types 1 and 2, antibody prevalence was close to or above 90% in the majority of age groups. For poliovirus type 3, antibody prevalence was below 80% in teenagers and young adults. Our study shows that the Portuguese are well protected against poliovirus types 1 and 2. For poliovirus type 3, the suboptimal antibody levels observed in teenagers and young adults suggest the need for a booster dose to minimise the risk of wild poliovirus importation.

The HPV Vaccine

In 1999, the Morbidity and Mortality Weekly Report (MMWR) identified the ten most significant public health achievements of the last 100 years (Table 1). (1) First on the list of accomplishments was vaccination, a biomedical and public health success story responsible for saving millions of lives and preventing untold misery from infectious diseases. Both life expectancy and quality of life have improved because of vaccines that have eradicated diseases such as smallpox, and virtually eliminated childhood diseases such as measles, diphtheria and pertussis (whooping cough). A particularly good example of the impact of vaccines are ones developed to combat infantile paralysis (polio), first by Salk, and later, by Sabin. Between 1951 and 1954, immediately prior to the widespread dissemination of Salk's polio vaccine, there were over 16,000 cases of paralytic poliomyelitis, and an average of 1900 U.S. deaths annually from polio. (2) The Salk vaccine was licensed in the U.S. in 1955, and cases of the disease dropped precipitously to fewer than 1000 per year until 1962, when the Sabin vaccine was licensed and administered on a widespread basis. (2) By the end of 1962, fewer than 100 cases were seen annually. There has not been a naturally occurring case of polio in the United States since 1979. (3) Concerted efforts by health and non-profit organizations to disseminate the polio vaccine have reduced the global burden of polio from approximately 350,000 cases per year in the late 1980s to 1200 cases in 2005, the 50th anniversary of the development of the vaccine. (4) A new vaccine has been developed and released for use against a leading cause of death in women worldwide--cervical cancer. The human papillomavirus, or HPV, a species-specific DNA virus with over 100 types identified to date, has been recognized as the causal agent in the development of cervical cancer. It also is associated with other cancers (e.g., anal, penile, vulvar, vaginal, and oral-pharyngeal). Over 30 types of HPV are anogenital, and approximately half of those are oncogenic. If left untreated, they have the ability to progress to invasive cancers. Other anogenital HPV types, known as low-risk types, are responsible for genital warts. Whereas genital warts are benign, they are visible and may be a source of embarrassment. HPV is common--a recent U.S. study concluded that overall prevalence among 14-24 year-old women, an age group included in the age range targeted for the HPV vaccine, is 33.8%, and that: This prevalence corresponds with 7.5 million females with HPV infection, which is higher than the previous estimate of 4.6 million prevalent HPV infections among females in this same age group in the United States. (5(p817)) Furthermore, the lifetime likelihood of acquiring HPV is estimated to be 75% or more. (6) Fortunately, infection with HPV also is transient, and in most cases, will clear up through the body's own immune response. According to the National Cancer Institute, about 10% of women have an oncogenic HPV infection at a given time, and they are more common in young women than in older women. Most cervical infections, including ones involving oncogenic types of HPV, clear on their own without causing cancer. (7) In the U.S., cervical cancer incidence and deaths have significantly decreased because of a well-designed and effective screening program, with an estimated number of 11,150 invasive cervical cancer cases, and 3670 deaths forecast for 2007. (8) Globally, the picture is grim as more than 250,000 women die annually from cervical cancer, making it the second most common cause of cancer death in women. Moreover, the World Health Organization anticipates a 25% increase in cervical cancer deaths over the next decade if significant interventions do not occur. (9) In addition, 80% of the approximately half million women who will be diagnosed with cervical cancer worldwide live in resource-poor developing countries that do not have the infrastructure to provide cytology screening for the disease. …

Protective efficacy of a monovalent oral type 1 poliovirus vaccine: a case-control study

A high-potency monovalent oral type 1 poliovirus vaccine (mOPV1) was developed in 2005 to tackle persistent poliovirus transmission in the last remaining infected countries. Our aim was to assess the efficacy of this vaccine in India. We estimated the efficacy of mOPV1 used in supplementary immunisation activities from 2076 matched case-control pairs of confirmed cases of poliomyelitis caused by type 1 wild poliovirus and cases of non-polio acute flaccid paralysis in India. The effect of the introduction of mOPV1 on population immunity was calculated on the basis of estimates of vaccination coverage from data for non-polio acute flaccid paralysis. In areas of persistent poliovirus transmission in Uttar Pradesh, the protective efficacy of mOPV1 was estimated to be 30% (95% CI 19-41) per dose against type 1 paralytic disease, compared with 11% (7-14) for the trivalent oral vaccine. 76-82% of children aged 0-23 months were estimated to be protected by vaccination against type 1 poliovirus at the end of 2006, compared with 59% at the end of 2004, before the introduction of mOPV1. Under conditions where the efficacy of live-attenuated oral poliovirus vaccines is compromised by a high prevalence of diarrhoea and other infections, a dose of high-potency mOPV1 is almost three times more effective against type 1 poliomyelitis disease than is trivalent vaccine. Achieving high coverage with this new vaccine in areas of persistent poliovirus transmission should substantially improve the probability of rapidly eliminating transmission of the disease.

Eradication versus control for poliomyelitis: an economic analysis

Worldwide eradication of wild polioviruses is likely to yield substantial health and financial benefits, provided we finish the job. Challenges in the four endemic areas combined with continuing demands for financial resources for eradication have led some to question the goal of eradication and to suggest switching to a policy of control. We developed a dynamic model, based on modelling of the currently endemic areas in India, to show the importance of maintaining and increasing the immunisation intensity to complete eradication and to illustrate how policies based on perception about high short-term costs or cost-effectiveness ratios without consideration of long-term benefits could undermine any eradication effort. An extended model assesses the economic implications and disease burden of a change in policy from eradication to control. Our results suggest that the intensity of immunisation must be increased to achieve eradication, and that even small decreases in intensity could lead to large outbreaks. This finding implies the need to pay even higher short-run costs than are currently being spent, which will further exacerbate concerns about continued investment in interventions with high perceived cost-effectiveness ratios. We show that a wavering commitment leads to a failure to eradicate, greater cumulative costs, and a much larger number of cases. We further show that as long as it is technically achievable, eradication offers both lower cumulative costs and cases than control, even with the costs of achieving eradication exceeding several billion dollars more. A low-cost control policy that relies only on routine immunisation for 20 years with discounted costs of more than $3500 million could lead to roughly 200 000 expected paralytic poliomyelitis cases every year in low-income countries, whereas a low-case control policy that keeps the number of cases at about 1500 per year could cost around $10 000 million discounted over the 20 years. Focusing on the large costs for poliomyelitis eradication, without assessing the even larger potential benefits of eradication and the enormous long-term costs of effective control, might inappropriately affect commitments to the goal of eradication, and thus debate should include careful consideration of the options.

Polio eradication in India: The way forward

Despite remarkable decline in the number of poliomyelitis cases, the dream of polio eradication in India remains elusive. This is despite considerable effort and expenditure for well over a decade. Various reasons have been cited for this and interventions implemented accordingly. None of these seem to have borne fruit. It is appropriate to have a relook at the polio eradication strategies in order to learn from past errors and determine a feasible solution to achieve the goal. This article examines important tissues that hamper the eradication effort and proposes a way forward.

Use of mutational pattern in 5′-NCR and VP1 regions of polioviruses for molecular diagnosis

Polioviruses are members of the enterovirus genus, belonging to the Picornaviridae family. They are the causative agents of poliomyelitis, a paralytic and sometimes fatal disease in humans. The number of poliomyelitis cases caused by wild poliovirus infections has been dramatically reduced by the extensive use of two available vaccines: the inactivated poliovirus vaccine (IPV) and the oral poliovirus vaccine (OPV). Despite the importance of OPV in the reduction of poliomyelitis cases, one of the disadvantages associated with this vaccine is the rare occurrence of vaccine-associated paralytic poliomyelitis (VAPP) in vaccinees or their healthy contacts through the accumulation of mutations and/or recombination in Sabin strains genome. Thirteen clinical isolates originating from healthy vaccinees and VAPP cases were investigated in order to identify genomic modifications in 5' non-coding region (5'-NCR) and VP1 genomic regions. The analysis of samples was conducted by RT-PCR, RFLP, sequencing and bioinformatics analysis. All clinical isolates were characterized as OPV-like viruses. Our results showed that analysis of 5'-NCR and VP1 regions of Poliovirus Sabin strains is important in order to identify mutations that increase the neurovirulence conducting to the eventuality of emergence of VAPP cases.

Results of modified Robert Jones operation for clawed hallux.

The results of modified Robert Jones operation for clawed hallux carried out on 36 feet were reviewed by clinical and radiological investigations. Twenty-nine feet (80 per cent) achieved good results while 3 feet (8-5 per cent) obtained fair results and in 4 feet (11 per cent) the results were poor. Better results were obtained in the poliomyelitis cases than in the other groups. Correction of deformity appears to be achieved by the transferred extensor hallucis longus elevating the first metatarsal neck and by the flexor hallucis longus flexing the rigid toe obtained by interphalangeal arthrodesis. Tendon regeneration which is associated with recurrent clawing remains a problem. Internal fixation should be used for the interphalangeal arthrodesis.

VACCINE-DERIVED POLIOVIRUSES AND THE ENDGAME STRATEGY FOR GLOBAL POLIO ERADICATION

As the global eradication of wild poliovirus nears, the World Health Organization (WHO) is addressing challenges unprecedented in public health. The live, attenuated oral poliovirus vaccine (OPV), used for more than four decades to interrupt poliovirus transmission, and the vaccine of choice for developing countries, is genetically unstable. Reversion of the small number of substitutions conferring the attenuated phenotype frequently occurs during OPV replication in humans and is the underlying cause of the rare cases of vaccine-associated paralytic poliomyelitis (VAPP) in OPV recipients and their close contacts. Whereas VAPP has long been recognized, two other adverse events have been identified more recently: (a) long-term excretion of highly evolved vaccine-derived polioviruses (VDPVs) in persons with primary immunodeficiencies, and (b) polio outbreaks associated with circulating VDPVs in areas with low rates of OPV coverage. Developing a posteradication strategy to minimize the risks of VDPV emergence and spread has become an urgent WHO priority.

Vaccine policy changes and epidemiology of poliomyelitis in the United States.

The last case of poliomyelitis in the United States due to indigenously acquired wild poliovirus occurred in 1979; however, as a consequence of oral poliovirus vaccine (OPV) use that began in 1961, an average of 9 cases of vaccine-associated paralytic poliomyelitis (VAPP) were confirmed each year from 1961 through 1989. To reduce the VAPP burden, national vaccination policy changed in 1997 from reliance on OPV to options for a sequential schedule of inactivated poliovirus vaccine (IPV) followed by OPV. In 2000, an exclusive IPV schedule was adopted. To review the epidemiology of paralytic poliomyelitis and document the association between the vaccine schedule changes and VAPP in the United States. Review of national surveillance data from 1990 through 2003 for cases of confirmed paralytic poliomyelitis. Number of confirmed paralytic poliomyelitis cases, including VAPP, and ratio of VAPP cases to number of doses of OPV distributed that occurred before, during, and after implementation of policy changes. From 1990 through 1999, 61 cases of paralytic poliomyelitis were reported; 59 (97%) of these were VAPP (1 case per 2.9 million OPV doses distributed), 1 case was imported, and 1 case was indeterminate. Thirteen cases occurred during the 1997-1999 transitional policy period and were associated with the all-OPV schedule; none occurred with the IPV-OPV schedule. No cases occurred after the United States implemented the all-IPV policy in 2000. The last imported poliomyelitis case occurred in 1993 and the last case of VAPP occurred in 1999. The change in polio vaccination policy from OPV to exclusive use of IPV was successfully implemented; this change led to the elimination of VAPP in the United States.

Phylogenetic analysis of wild-type 1 polioviruses isolated during the final period of transmission in Turkey

The last poliomyelitis case associated with a wild poliovirus in Turkey occurred in November 1998. This was the last known case of paralytic poliomyelitis caused by indigenous wild poliovirus in the World Health Organization's European Region. This study investigated the genetic relationships of wild-type 1 polioviruses at the latest period of transmission. A phylogenetic tree was constructed on the basis of the VP1/2A sequence from 14 wild-type 1 polioviruses isolated from Turkey in 1994-1998, along with those from other areas of the world. The Turkey isolates in the latest period of transmission were closely related to each other, forming a cluster distinct from other strains. The results showed that these viruses had been spreading indigenously in the eastern and south-eastern parts of Turkey, and ceased transmission there during 1998. This finding serves as a reference for future poliovirus surveillance both in Turkey and worldwide.

Polio eradication, cessation of vaccination and re-emergence of disease.

The poliovirus eradication programme coordinated by the World Health Organization mainly involves immunization with a live attenuated vaccine. Only six countries — India, Pakistan, Afghanistan, Egypt, Nigeria and Niger — still have endemic poliovirus. To tackle recent outbreaks in India and Nigeria, eradication strategies have been refocused. It was hoped that complete eradication of wild-type poliovirus would be achieved by the end of 2003, but during 2004 there have been setbacks to polio immunization in Nigeria, and the number of poliomyelitis cases has increased. It still seems possible that the virus could be eradicated — but should vaccination continue when that goal has been achieved?

Five-year surveillance of acute flaccid paralysis in Malaysia.

The nation-wide surveillance for acute flaccid paralysis (AFP) was implemented in Malaysia in 1995 and further intensified in 1996 as part of the World Health Organization's (WHO) certification process for polio eradication in the Western Pacific Region. Clinical data on AFP cases during a 5-year surveillance period from 1997 to 2001 were compiled and analysed. Based on 517 cases of AFP reported during this 5-year period, the overall rate of AFP was 1.2 per 100 000 children below 15 years old. The major clinical diagnosis associated with AFP were Guillain-Barre syndrome (30.2%), central nervous system infection (16.2%), transverse myelitis (10.6%) non-polio enterovirus infection (6.2%), and hypokalaemic paralysis (5.2%). This unusual pattern with an excess of CNS infection and non-polio enterovirus infection was attributed to the outbreak of enterovirus 71 infection nation-wide in 1997. According to the WHO virological classification, there was no case of poliomyelitis due to wild poliovirus. Three cases were 'polio compatible', there were no cases of vaccine-associated paralytic polio (VAPP), while 62 cases (12.0%) were merely classified as 'non-polio AFP'. Overall, these data suggest the absence of circulation of wild poliovirus in Malaysia from 1997 to 2001. The pattern of AFP in this study is different from other published reports.

Retrospective study on poliomyelitis cases in northern Greece

Here we report the results of a retrospective study on the epidemiological characteristics and genetic relationships of the virus isolates responsible for the last poliomyelitis cases in Greece. The last wild poliomyelitis case in Greece was detected in 1996, and the last vaccine-related strain was isolated in 1998. The whole of Europe, including Greece, is now considered to be polio-free.

Acute flaccid paralysis

Poliomyelitis is an acute viral infection caused by RNA virus. It is primarily an infection of the human alimentary tract but the virus may infect the central nervous system in a very small percentage (1%) of cases resulting in varying degrees of paralysis, and possibly death [1]. The extensive use of polio vaccines since 1954 has virtually eliminated the disease in developed countries. The South East Asia Region (SEAR) contains the largest remaining reservoir of wild polio virus in the world. The incidence of reported poliomyelitis cases has declined by 90% [2]. In this era of eradication of polio, even a single case is treated as an outbreak and preventive measures should be initiated, usually within 48 hours of notification of the case [3]. One of the most important and major objectives of Nation wide Polio Eradication programme is to ensure timely and complete reporting of cases of acute flaccid paralysis (AFP) and to collect stool specimen within 14 days and conduct outbreak response immunisation (ORI) as early as possible. Here we report one case of AFP which was diagnosed, notified, investigated and managed within 8 hours and stool specimen collected within 48 hours of reporting of the case. The case was epidemiologically investigated as per the Ministry of Health and Family Welfare and WHO guidelines and ORI was conducted in the community next day. The response in this case not only shows coordinated effort of curative and preventive medicine but how health teams of civil and army should function in cohesion to curb any public health problem.

Detection of viral sequences in archival spinal cords from fatal cases of poliomyelitis in 1951–1952

Poliovirus (PV) subjected to genetic characterization is often isolated from faecal carriage. Such virus is not necessarily identical to the virus causing paralytic disease since genetic modifications may occur during replication outside the nervous system. We have searched for poliovirus genomes in the 14 fatal cases occurring during the last epidemics in Norway in 1951–1952. A method was developed for isolation and analysis of poliovirus RNA from formalin-fixed and paraffin-embedded archival tissue. RNA was purified by incubation with Chelex ®-100 and heating followed by treatment with the proteinase K and chloroform extraction. Viral sequences were amplified by a reverse transcriptase-polymerase chain reaction (RT-PCR), the products subjected to TA cloning and sequenced. RNA from the β-actin gene, as a control, was identified in 13 cases, while sequences specific for poliovirus were achieved in 11 cases. The sequences from the 2C region of poliovirus were rather conserved while those in the 5′-untranslated region were variable. The developed method should be suitable also for other genetic studies of old archival material.

Prolonged detection of indigenous wild polioviruses in sewage from communities in Egypt.

Environmental surveillance for polioviruses has been implemented in Egypt. This paper reports on a study in which 130 sewage samples were collected between January 2001 and December 2001 from eight provinces of Egypt. Samples were analyzed by virus isolation in L20B and RD cell cultures, and wild polioviruses were characterized by sequencing of the VP1 protein coding region. Wild type 1 polioviruses were detected in 57% of the sewage samples and 91% of the study sites, only two of which reported paralytic poliomyelitis cases in 2001. Three genetic lineages of a single indigenous type 1 poliovirus genotype were detectable in sewage, and only one lineage was also detected through surveillance for acute flaccid paralysis. Wild polioviruses persisted in the environment despite implementation of oral poliovirus vaccine immunization campaigns. Continued analysis of sewage samples, critical evaluation of immunization coverage, and performance of surveillance for acute flaccid paralysis are proposed as follow-up activities.

Polio eradication: the OPV paradox.

Routine and mass administration of oral polio vaccine (OPV) since 1961 has prevented many millions of cases of paralytic poliomyelitis. The public health value of this inexpensive and easily administered product has been extraordinary. Progress of the Global Polio Eradication Initiative has further defined the value of OPV as well as its risk through vaccine-associated paralytic poliomyelitis (VAPP) and vaccine-derived polioviruses (VDPV). Although both are rare, once wild poliovirus transmission has been interrupted by OPV, the only poliomyelitis due to poliovirus will be caused by OPV. Poliovirus will be eradicated only when OPV use is discontinued. This paradox provides a major incentive for eventually stopping polio immunization or replacing OPV, but it also introduces complexity into the process of identifying safe and scientifically sound strategies for doing so. The core post eradication immunization issues include the risk/benefits of continued OPV use, the extent of OPV replacement with IPV, possible strategies for discontinuing OPV, and the potential for development and licensure of a safe and effective replacement for OPV. Formulation of an informed post eradication immunization policy requires careful evaluation of polio epidemiology, surveillance capability, vaccine availability, laboratory containment, and the risks posed by the very tool responsible for successful interruption of wild poliovirus transmission.