Please could you tell us a little bit about Polio and who it affects?
Polio is a disease caused by a virus and results in paralysis, usually in the legs, of those affected. The paralysis is irreversible. In some extreme cases the virus spreads to the nerve cells of the brain reducing breathing capacity and this rarer form can be fatal.
Infection with the virus mainly affects children under five and causes paralysis in about one in 200 cases, the rest being infected but not presenting with signs of disease (asymptomatic).
In most parts of the world polio has been eliminated by sustained vaccination programmes in the late 20th century. Afghanistan and Pakistan are among only three countries – along with Nigeria – that have never managed to eliminate polio.
Why, other than to prevent the potential paralysis caused by polio, is polio eradication in these countries so important?
To those individuals and families affected by polio, the disease can be life threatening, and for all the disease has a huge affect on their quality of life.
The Polio Eradication Initiative, consisting of partners such as Rotary, WHO, CDC and Unicef, coordinate the surveillance and vaccination activities for polio, and the Initiative is one of the largest public health initiatives globally. It was a brave step to commit to eradication of polio in 1988, and it is important to show that eradication through vaccination is possible for diseases other than smallpox.
By vaccinating children, largely using the oral polio vaccine (OPV), the Initiative has gone a long way to strengthening routine vaccination services in all countries, including in Afghanistan and Pakistan. So even before the last case of polio in these countries, more children will be vaccinated against measles, TB, and other serious childhood infections as the capacity for local health services has been strengthened through investment and training of people in the healthcare sector.
What has hindered Polio eradication so far?
In Pakistan and Afghanistan, polio eradication faces many issues; in the paper we report that since 2006 vaccination coverage in Balochistan and the Federally Administered Tribal Areas (FATA) in Pakistan and Southern Afghanistan has declined, resulting in fewer children reporting four or more doses of the OPV.
The reasons for this are many, and vary from region to region. To achieve high coverage in mass campaigns volunteers are often required to move house-to-house to vaccinate children rather than using fixed posts.
This requires knowledge of where people live, large numbers of volunteers and tight oversight of operations. This can be particularly difficult in regions affected by conflict and natural disasters, such as Afghanistan and Pakistan.
Why have too few children received sufficient doses of the vaccine? Is this due to not enough being available; scares over the safety of the vaccine, or other reasons?
Whilst vaccine stocks are plentiful, it can become difficult to reach all children in a population. The main issues in Afghanistan and Pakistan are poor management and accountability and inaccessibility due to conflict.
The Eradication Initiative relies on thousands of volunteer vaccinators to distribute the vaccine during mass immunisation days. Careful planning is required to identify fixed posts in villages and also ensure that houses are visited during house-to-house campaigns.
All vaccinators require training to ask the right questions when visiting each house. Especially in Afghanistan, armed conflict has affected the accessibility of some areas to vaccinator teams. Here, local information is required to assess the safety of vaccinators and sometimes careful negotiations are required with anti-governmental elements to obtain access.
Although the OPV is one of the safest vaccines ever developed, concerns over its safety occasionally arise, largely from erroneous sources. In these instances local health care workers engage with the community to listen to their concerns, and assist them to understand the health benefits of vaccination.
It was recently reported in the news that a newly introduced bivalent oral poliovirus vaccine (OPV) could eliminate polio in the countries in which it is still present. Please could you tell us what an OPV is and what is so new about it which means that it may help to eradicate polio?
The standard polio vaccine is the trivalent OPV, meaning that this vaccine protects against all three poliovirus serotypes. The advantage is that one vaccine protects against all three but it comes at a cost as the protective efficacy is relatively low (12.5% efficacy in Pakistan and Afghanistan), meaning that for all children that have only received one dose of the OPV 12.5% will be protected from disease.
The bivalent protects against serotype 1 and 3, which are the remaining 2 circulating wild virus types. As the vaccine focuses on protecting against these two virus types, the efficacy is higher (23.4% efficacy against serotype 1). The difference in efficacy means that fewer doses are needed for population immunity to be high enough to prevent circulation of wild virus – and local elimination becomes more likely.
Do you think polio eradication is an achievable task, and how soon do you think it could be achieved?
It’s definitely WHEN, not IF! I think India achieved an amazing goal of eliminating polio last year, and this was done through vaccinating millions of children annually. India has shown us all that polio eradication is achievable.
2012 will be a pivotal year for Afghanistan and Pakistan as both have announced country-specific plans to improve vaccination coverage, even in the hard to reach areas. Should the targets of 90% coverage of children with >3 OPV doses be met in Pakistan and Afghanistan this year, the cases will drop and elimination of polio in each country will become a reachable goal.
Are there plans to carry out future research into this field?
Yes, the Vaccine Epidemiology group at Imperial College consists of several researchers that look into specific questions surrounding polio elimination. An important component in Afghanistan and Pakistan is accurate estimates of vaccine coverage, and I am working on this in collaboration with the WHO.
We also need to know about the success of different vaccination strategies, how best to choose from the different available vaccines, and which regions of Afghanistan and Pakistan would benefit most from vaccination campaigns.
Where can readers find more information?
They can find more information in our paper: http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(12)60648-5/abstract
They can visit our group website at Imperial College:
http://www1.imperial.ac.uk/medicine/research/researchthemes/infection/ide/research_groups/vaccineepidemiology/
About Dr. Kathleen O’Reilly
Dr Kathleen M O’Reilly is a post-doctoral researcher at Imperial College London, in the Medical Research Council Centre for Outbreak Analysis and Modelling. She has recently been awarded a Medical Research Council Fellowship in Methodology Research.
Kathleen specialises in the use of mathematical and statistical models to provide insight to the control of infectious diseases. She currently focuses on the control and eradication of poliomyelitis, in collaboration with the World Health Organisation. Her research examines current control efforts in Africa and Asia.
Recent publications include a statistical model to predict and prevent polio outbreaks in Africa, and a retrospective analysis of the protective efficacy of the OPV in Pakistan and Afghanistan and the effect of immunisation on polio incidence in these countries. She has recently returned from Afghanistan where she was a member of an independent mission to understand the drivers of poliomyelitis in 2011.
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