RICERCA ITALIANA     

NEED OF VIROLOGICAL AND SEROLOGTICAL SURVEILLANCE OF THE ITALIAN POPULATION DURING THE FINAL STEPS OF WORLDWIDE ERADICATION OF POLIOMYELITIS

Università degli Studi di Roma "La Sapienza"

Abstract

The WHO Polio Eradication Strategic Plan 2004-2008 revises timeframe for certification of eradication and outlines the key polio eradication activities: 1) Interruption of Poliovirus Transmission Phase (2005-2006?); 2) Global Certification and Mainstreaming Phase (2006-2008); OPV Cessation Phase (from 2009). The major issue is the rapid interruption of polio transmission in Nigeria, India, Pakistan, Niger, Afghanistan and Egypt. While in endemic areas the priority is to ensure NIDs and sNIDs, in polio free areas the emergency could be represented by wild poliovirus importation and/or circulating VDPVs. Today, the emergency regards the countries bordering Nigeria: in Africa the emergency is due to the fact that the imported strain begins to circulate in countries where the routine coverage of vaccination is low. The recent cases in Saudi Arabia and Ethiopia show that nobody can feel safe, even after years of wild polio strain absence The globalization of tourism and migrations can represent a risk of reintroducing wild poliovirus or OPV or cVDPV into polio free countries, Italy included, where, starting 2002, children are vaccinated with IPV to eliminate the OPV paradox. The only concern is the absence of mucosal immunity that could permit again poliovirus circulation. Actually, the Italian situation can be considered optimal: no polio cases, no VAPP, good vaccination coverage, but in the same time Italy is a high risk country for the reason just illustrated. If the risk of importing wild poliovirus could be progressively vanishing, the risk of importing OPV and/or VDPV is consistent. Previous Italian surveys which have been repeated on a regional and nation-wide scale, have brought to light sabin-like strains retro mutated to neurovirulence. In an Italian study in 2000 (vaccination schedule OPV-IPV), Sabin-like viruses were found in 93 out of 5714 (1.6%) samples of faeces from healthy children. It is noteworthy that a substantial proportion of youngsters aged 10-15, who completed vaccination many years before, shed sabin-like strains. Also from environmental samples, retromutated poliovirus 2 and 3 were isolated.
After certification of European Region as polio free, the Italian Ministry of Health has approved a national action plan, prepared in accordance with the WHO instructions, which detailed objectives and actions to maintain the polio-free status of the country. One of the objectives was to maintain a high vaccine coverage to avoid possible cases due to the reintroduction of a wild strain or even to the circulation of VDPV.
Due to the pathogenic potential of VDPVs the rapid identification of their presence in the population and its timely notification could become part of the activities to be implemented in the post-certification era at national and international levels.
The goals of the present project are:
1. the serological surveillance of children 0-14 y
2. the virological surveillance of Sabin-like virus or VDPV in healthy children (0-14 y old): stool survey
3. the virological surveillance in the environment (sewage and/or surface waters) after 2 years from OPV vaccination interruption.
4. The virological and serological surveillance of foreign children who were recently adopted by Italian families.
Analyses will be carried out as suggested by WHO for virological and serological surveys, and its performance indicators will be adopted.
Expected results: As polio is not endemic in Italy, the isolation of wild poliovirus strains is unlikely. Today, it is more likely that OPV will be isolated, even if a lesser percentage of positive samples is expected.
The qualification of all the Research Units participating in the present project is documented by their role as reference units for the respective region within the AFP National Surveillance Net and also by their recognition by WHO as a Sub-National Virological Reference Laboratory. The Milan Unit is participating to the international quality controls for PCR. <<<

Principal Investigator

Gaetano Mario Luigi FARA Università degli Studi di ROMA "La Sapienza"

Research Objectives

The present study is a public health surveillance, and as such it deserves standardized methods, so that results can be compared at national and international level. Some modiications have been introduced but always in comparison with the standard methods, and an international comparison is compuolsory before adoption. The study is to be performed in two steps: phase 1 (18 months): organization of the survey, enrollment of the children, environmental sampling and analysis performance. Phase 2 includes statistical analysis of the results, interpretation and preparation of the report.
The enclosed scheme reports the distrribution of the work to the different units and the level of integration among them.
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The goals of the present project are:
1. the surveillance of italian children aged 0-14 y;
2. the virological surveillance of Sabin-like virus or VDPV in healthy children (0-14 y old): stool survey
3. the virological survey in the environment (sewage and/or surface waters), 3 years after OPV vaccination interruption.
4. The virological and serological surveillance of foreign children of recent adoption by Italian families
Goal 1: the last national serological survey performed in 2000-2001 has involved 10054 subjects aged 0-40 (2571 children 0-15; 7483 people 17-40) enrollede through all the italian regions. Results have shown a protection of 93.1% - polio 1 -, 92.7% - polio 2 -, 877.1% - polio 3 v-. Subjects lacking antibody for 1 or more poliovirus belonged mostly to class 20-30 y in all the regions; children 0-15 y showed a protectioon of 97.3% (polio 1), 96.6 (polio 2) and 92.7% (polio 3). Analyzing the regoionaql diffreernces, it has been shown that: (1) the percentage of subject fully unprotected ranged between 2 and 10%, and this is probably due to the unaccuracy in vaccination schedules applied in the different regions; (2) in some regions the level of unprotection toward polio 3 is similar to the one to polio 1 and 2, while in others is higher (eg Lombardy 13.8%, Apulia 17.4%). Suchdata rrequire a revision of the sureveillance atr the ages 0-14, in order to verify whether (1) the vaccination by a 6-valent vaccine provides high antibody levels and (2) whether the percentage of subjects with low or non-detectable antibody increases in abvsence of boosrer doses previously provided by OPV.

Goal 2: Surveillance for acute flaccid paralysis (AFP) in children 0-14 years, and careful investigation of the cases, are the gold standard for monitoring the progress of the poliomyelitis eradication programme. Italy implemented AFP surveillance since 1997, but its sensitivity to detect wild poliovirus circulation is minimal, due to the fact that polio incidence is zero. No real alternative approach, which is generally exploitable, has been developed worldwide yet.
Enterovirus surveillance, based on the examination of stool specimens of healthy children, may be an approach to supplement AFP surveillance in country polio free as Italy, a country where the risk of importation of wild poliovirus is still real, as wild poliovirus is still circulating in some countries of neighbouring regions. The same problem exists for OPV and VDPV, which are responsible for more than one epidemic in polio-free countries.
Further, previous Italian surveys which have been repeated on a regional and nation-wide scale, have brought to light sabin-like strains retro mutated to neurovirulence. In an Italian study in the year 2001 (vaccination schedule IPV-OPV), Sabin-like viruses were found in 93 out of 5714 (1.6%) samples of faeces from healthy children. It is noteworthy that a substantial proportion of youngsters aged 6-15, many years after the completion of OPV vaccination, shed Sabin-like strains.
The modification of the vaccination schedule, introduced in 2002, involves immunization only with IPV so it is nearly three years that the attenuated live vaccine is no more in use. This means no more polio vaccine viruses are being introduced into the population, so the virus should no longer be in circulation. One consequence of IPV vaccination, however, is that there is a gradual accumulation of people with inadequate mucosal immunity, who could acquire the infection, but not the disease, permitting replication of the virus in their intestine and its elimination; once it starts to circulate, this virus could accumulate mutations, leading to strains that are biologically different from the attenuated parent strains.
Due to the pathogenic potential of VDPVs the rapid identification of their presence in the population and their timely notification could become part of the activities to be implemented in the post-certification era at national and international levels.
The stool surveillance of healthy children may provide additional information on the circulation of other enteric non-polio enteroviruses.
Goal 3:
Environmental surveillance is making an important contribution to wild poliovirus surveillance with detection of wild virus in the absence of detected paralytic case in the same area. In Italy it may also contribute to provide valuable supplementary information and available data for decision making about post-certification immunization policies as it will be used as a tool to monitor silent circulation of vaccine strains in the environment following a change in immunization practice from OPV to IPV use in our country. The plan for environmental surveillance, as suggested by WHO, include
1. duration and time schedule of sampling
2. details of sampling sites (location and population sizes to be represented)
3. protocols for sample processing and virus identification
4. data management and reporting.

Sampling frequency should be twice a month; sampling sites will be at inlets of sewage treatment plants or other major collector sewers. As industrial wastes may contain compounds that may be toxic to cell cultures and interfere with viral replication, plants will be selected which process domestic waste only. The most convenient size of source population will be 100,000 – 300,000. Unit 1 (Latium) will analyze samples collected in all counties, and for Rome the analysis will incude all sewers and of the river Tiber.

In Italy, the population groups at risk are represented almost by gipsy communities. In Rome gipsies live in camps difficult to control and dispersed in several sections of the town. When such camps are equipped with public toilets, the outcoming waste gets mixed with the waste from the rest of population. However, it is important to outline that in Rome NIDs for the gipsie have been already performed in the 2003.

Goal 4
Foreign children in adoption by Italian parents mostly come from Latin America, Africa, Eastern Europe and South West Asia, and have been previously vaccinated in their original countries using OPV, often administered during NIDs and subNIDs. If, after leaving the original family, they have been assisted by other families or by institutions, dependable data are available; but if they have been abandoned, data about growth, vaccinations, previous diseases, will be lacking. In that case the viral and sero surveillance will be precious to verify the immune status and the virus shedding. Such a problem is important in Emilia-Romagna, a region that in the present project is responmsible for such investigation.
The qualification of all the Research Units participating in the present project is documented by their role as reference unit for the respective region within the AFP National Surveillance Net and also by their recognition by WHO as a Sub-National Virological Reference Laboratory. The Milan Unit is participating to the international quality controls for PCR. <<<

Timescale

24 months

National and international background

By bike or just walking, an army of 28,000 volunteers rushes through cities and villages of Ivory Coast with the goal of vaccinating ALL the children. The same scene takes place in at least 17 more countries of Africa, 3 of which are endemic and 14 more are suffering again from paralytic poliomyelitis due to the reintroduction of wild polioviruses. In Africa is "red" emergency: after 18 years of hard work, the expected final phase of polio eradication is apparently ranning away. But says David Heyman - in charge for WHO of polio eradication project - we are not allowed to be pessimistic, we must be convinced that al last the poliovirus will be wiped off by 2005, or we are condemned to a definite failure.
Poliomyelitis is an infectious disease caused by any one of three related enteroviruses: poliovirus types 1, 2, or 3. It can strike at any age, but, in more than 50% of all cases, affects children under 3. The disease causes paralysis, which is almost always permanent as the virus destroys motor neurons. The leg muscles are affected more often than the arm's. The limb becomes floppy and lifeless - a condition known as Acute Flaccid Paralysis (AFP). More extensive paralysis can result in quadriplegia. In the most severe cases (bulbar polio), poliovirus attacks the motor neurons of the brain stem - reducing breathing capacity and causing difficulty in swallowing and speaking. Without respiratory support, bulbar polio can result in death. Polio has probably caused paralysis and death for most of human history. The oldest clearly identifiable reference to paralytic poliomyelitis is an Egyptian stele over 3,000 years old (the Ruma stele in a Copenhagen museum). Cases of poliomyelitis tended to be rare in ancient times, though, as sanitation was generally poor. With improvements in waste disposal and the widespread use of indoor plumbing in the 20th century, epidemics of polio began to occur with regularity in the developed world, primarily in cities in summertime. Because sewage was dumped away from the drinking water supply, babies were much less likely to be infected with polio and therefore to gain protective immunity. As the children got older and began playing with others, swimming in public pools, and going to school, they were exposed to the virus, which was then more likely to cause paralytic poliomyelitis. Large polio epidemics caused panic every summer during the '40's and the '50's in industrialized countries (US, Western Europe) and crippled thousands of children every year. Soon after the introduction of effective vaccines in the late '50s (IPV) and early '60s (OPV), polio was brought under control, and practically eliminated as a public health problem in industrialized countries. It took somewhat longer for polio to be recognised as a major problem in developing countries. However, surveys during the '70's revealed that the disease was also frequent in developing countries, crippling thousands of children every year. As a result, during the '70's, routine immunization with OPV as part of national immunization programmes (Expanded Programme on Immunization, or EPI programmes) was introduced worldwide, helping to control the disease in many developing countries. In 1985, Rotary launched the PolioPlus program to protect children worldwide from the consequences of polio. In 1988, the World Health Assembly challenged the world to eradicate polio. The Global Polio Eradication Initiative is spearheaded by WHO, Rotary International, the US Centers for Disease Control and Prevention and UNICEF. The polio eradication coalition includes governments of countries affected by polio; private foundations (e.g. United Nations Foundation, Bill & Melinda Gates Foundation); development banks (e.g. the World Bank); donor governments (e.g. Australia, Austria, Belgium, Canada, Denmark, Finland, Germany, Ireland, Italy, Japan, Luxembourg, the Netherlands, New Zealand, Norway, Russia, the United Kingdom and the United States of America); the European Commission; humanitarian and nongovernmental organizations (e.g. the International Red Cross and Red Crescent societies) and corporate partners (e.g. Sanofi Pasteur MSD, De Beers). From the starting of the global poliomyelitis eradication initiative in 1988 until now, the number of countries where polio is endemic decreased from 125 to 6, and the number of reported polio cases decreased by >99% from an estimated 350,000 to 1263 in 2004. The result of 2004, excellent if just the figures are considered, represents a success in Asia but a failure in Africa. Wild type 2 poliovirus has not been detected worldwide since October 1999. The American and the Western Pacific Regions of the WHO have already been certified free of indigenous wild poliovirus. The European Regional Commission for Certification of Poliomyelitis Eradication (RCC) certified the WHO European Region polio-free on 21 June 2002. The six countries with indigenous wild poliovirus are: Nigeria, India, Pakistan, Egypt, Afghanistan, Niger. Additionally, in 2003 and 2004, polioviruses from endemic countries have been imported into polio-free contries, whose list is continuously growing: Sudan, Ethiopia, Mali, Saudi Arabia, Guinea, Tchad, Togo, Cameroun, CAR, Botsana, Burkina Faso, Ghana, Lebanon, Niger, Benin and Ivory Coast. After a eighteen-year effort that has galvanized more than 200 countries, 20 million volunteers, and requested an international investment of US$ 3 billion, the success or failure of the Global Polio Eradication Initiative, the world's largest public health campaign, is now within reach. Never before has the world been so close to success, with only six countries remaining polio-endemic. 2004 was expected to be the crucial year; actually the final success was apparently at hand, but it has not been achieved, and the present situation is at serious risk. The suspension in 2003 of OPV campaigns in the highly polio-endemic areas of northern Nigeria led to a marked increase in the number of reported cases from that country, resulting in WPV transmission in previously polio-free areas within Nigeria and importation of WPV into the quoted countries. The two clinical cases detected during the pilgrimage to Mecca in 2004 mean that in addition hundreds or even thousands of pilgrims got simply infected, but have fatally spread the virus into their countries of origin on their return home. Back in 2004, Dr Bruce Aylward, Global Co-ordinator Polio Eradication Initiative, WHO, had stated that Nigeria had become the major challenge on the road to global polio eradication. The persistent refusal of the OPV by northern Nigerian states with the highest rate of endemic polio implies that the intense wild poliovirus transmission in these states will continue unabated, posing a great risk to Nigeria's previously polio-free neighbours. This situation may have a serious impact on the eradication of poliomyelitis in the African Region.
Only repeated NIDs can help, but they are beginning to pose ethical problems, because they can cause several cases of VAPP. An additional challenge to efforts to eradicate polio worldwide is the finding that vaccine-derived polioviruses may circulate under suitable conditions. During 1988-1993, 32 polio cases associated with vaccine-derived poliovirus type 2 were found in 8 of 27 Governorates in Egypt. Although initial antigenic characterization of the isolates indicated that they had non-vaccine-like properties, nucleotide sequence analysis (i.e., comparing the 903 nucleotides encoding the major capsid protein, VP1) performed during 1999 revealed that all of the isolates were related (93%-96% nucleotide sequence identity) to the Sabin type 2 OPV strain (Sabin 2). The isolates were not related (less than 81% nucleotide sequence identity) to the wild type 2 poliovirus that had been indigenous to Egypt (last isolated in 1979) or to any other wild type 2 polioviruses. The isolates also differed from type 2 vaccine-derived polioviruses normally isolated from patients with acute flaccid paralysis that typically are related closely (>99.5% nucleotide sequence identity) to Sabin 2. Nucleotide sequence relationships among Sabin 2-derived polioviruses isolated in China during the mid-1990's also were consistent with the establishment of genetic lineages by person-to-person transmission. During the year 2000, circulation of type 1 vaccine-derived poliovirus (circulating VDPV [cVDPV]) in the Dominican Republic and Haiti was associated with 19 suspected polio cases associated with an outbreak of polio. Laboratory network activities were extended subsequently to include screening for these viruses, which have acquired wild-like neurovirulence and transmissibility and possess molecular characteristics that differentiate them from either vaccine or wild virus. Since January 2001, all poliovirus isolates are subjected to two methods of intratypic differentiation (ITD): one antigenic and one molecular. Concordant non-Sabin-like results are classified as wild polioviruses, concordant Sabin-like results are classified as Sabin-like (vaccine virus), and any discordant results or Sabin-like isolates lacking two tests are forwarded immediately for sequence analysis of the major viral capsid surface protein (VP1). These isolates are then classified based on the sequencing results: <1% difference from Sabin vaccine virus is classified as Sabin-like, 1%-15% difference is classified as VDPV, and >15% difference is classified as wild virus. The effectiveness of using this approach was demonstrated when three cases of AFP associated with cVDPV isolates were detected in the Philippines during March 2001.
So far sustained circulation of VDPV has been identified by serendipity on just these occasions, in populations where immunity was low. It is essential to undertake systematic searches to determine the frequency of sustained VDPV circulation.
In 2004, OPV which was and is the gold standard for immunization policies and which since 1961 has prevented many million cases of paralytic poliomyelitis may became the only poliomyelitis risk. OPV is the cause of 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.
In summary, current challenges to global polio eradication efforts include the persistent, intense transmission in northern India and some areas of western Africa, continued importations of wild poliovirus into polio-free areas, detection of circulating vaccine-derived poliovirus (cVDPV) and containment of laboratory strains. WHO suggests some Examples of the types of studies that may be useful
a. Prospective population based surveys for VDPVs, using alternative methods to the acute flaccid surveillance method used by the polio programme
b. Retrospective laboratory-based studies of polio isolates for markers of sustained circulation
c. Prospective population-based surveys of OPV circulation across OPV/inactivated polio vaccine (IPV) borders (time or geographic borders)
d. Development of laboratory procedures for post-immunization surveillance for polioviruses

Italy – State of Art
To obtain the consideration as a polio free country (remember that the declaration as polio free only pertains to an entire WHO Region), Italy had to demonstrate that there had been not a single case of poliomyelitis for a three years period, based on the evidence of the surveillance activity from every section of the Country, that poliovirus transmission has been interrupted.
The requirements for certification of elimination of wild poliovirus poses particular concerns because there has been no case detected for more than two decades. The last case of poliomyelitis in Italy, due to an indigenous wild poliovirus, was in a patient who developed paralysis in 1982. Since 1980, 3 imported cases – one each from Iran, India and Libya - have been reported. Thereafter, only a few vaccine-associated poliomyelitis cases were notified. Although indigenous wild poliovirus seems to be eliminated for several years, the risk of reintroduction will continue to be present, even if minimal, and this concern requires consequently an intense surveillance activity.
Acute flaccid paralysis (AFP) surveillance was started in 1996 and the integrative techniques such as surveillance of poliovirus, either in stool samples or in the water environment, were developed from this date. Also serosurveillance of immunity status against polioviruses in different age classes began to be performed systematically in that period to verify what is the immunitary coverage in Italian population (the Italian group who underwent compulsory OPV vaccination after 1964); also virological surveillance was developed to verify if there would be a circulation of wild poliovirus in Italy. After certification, the Ministry of Health has approved a national action plan, prepared in accordance to the WHO instructions, which detailed objectives and actions to maintain the polio-free status of the country. One of the objectives was to maintain a high vaccinal coverage to avoid possible cases due to the reintroduction of a wild strain or even to the circulation of vaccine-derived polioviruses (VDPV).
Recent innovations in Italian policy have been the replacement in 1999 of the full OPV by the sequential schedule (2 IPV + 2 OPV) and, after 2002 (Ministerial Decree 18 June 2002), by the full IPV schedule. This choice was motivated by the consideration that in absence of wild poliovirus indigenous circulation it was not ethical to accept the VAPP risk. Even if the choice is mandatory in a polio-free country, it is important to outline that mucosal immunity breaks down and this may be of public health concern when wild poliovirus or cVDPV would be imported or if OPV and derivatives still circulate in this Country.
In April 2005 an additional modification has been introduced by the recently approved National Vaccine Plan 2004-2006, which moves the 4th IPV dose (booster dose) from the 3rd to the 5th-6th year of age. This modification requests that an additional surveillance be introduced, to verify whether a reduction of protective level of antibodies takes place, due to the increase of the interval between the 3rd and the 4th dose of polio vaccine. <<<