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31 MAR 2016
Muhammad Zahir Hassan Nabil
icddr,b scientists have played a key role in helping Bangladesh achieve polio-free status, and continue to contribute to the global fight to eradicate the disease.
In March 2016, Bangladesh celebrates two years of polio-free status as declared by the World Health Organization (WHO) in March 2014. This declaration was made eight years after the last polio case had been reported in Bangladesh in 2006, following three decades of efforts to implement a polio immunisation strategy.
Infant receiving polio vaccine. Photo: CDC Global. CC BY 2.0
This immunisation strategy dates back to 1979, when the WHO reached out to Bangladesh to develop its expanded programme on immunisation (EPI) to eliminate deadly viruses, including poliovirus – notorious for causing irreversible paralysis and death amongst children.
Bangladesh is indebted to the international organisations, governments and scientists here and abroad for their support in expanding its EPI and the 21 National Immunization Days (NIDs). As part of the EPI drive, the NIDs played a huge role in achieving polio-free status. This countrywide immunisation drive was so successful that they were deemed no longer necessary from 2013 onwards.
It was the same momentous year in 2013 when Bangladesh’s battle against polio went beyond its borders as icddr,b lent its weight to the global drive to eliminate polio worldwide, signing up to the “Scientific Declaration on Polio Eradication”.
This Declaration endorsed the Eradication and Endgame Strategic Plan, developed by the Global Polio Eradication Initiative, which aims for a polio-free world by 2018. In order to achieve this, a comprehensive new strategy under the plan calls for wider participation across governments, international organisations and civil society.
Photo: Global Polio Eradication Initiative
It was an ambitious but timely initiative as reports of polio cases were waning across the world.
“As two deadly infectious diseases, smallpox and rinderpest, have been eradicated from the face of the earth, why polio should not be the third?” comments icddr,b senior scientist and epidemiologist Dr K Zaman, who has spearheaded most of the polio studies at icddr,b.
For several years, Dr Zaman and his colleagues have been carrying out studies on a range of oral polio vaccines (OPVs) in Bangladesh. “Until today icddr,b has conducted more than 10 polio vaccine studies on most polio vaccine variants,” says Dr Zaman. In addition, since 2005 they have contributed to the design of schedules for national immunisation programmes in Bangladesh.
Dr Zaman explains to us how icddr,b’s studies have contributed to the global goal to eradicate polio.
“The studies covering all rural, urban and suburban areas mostly looked at vaccine effectiveness,” he says. Some of the most important factors were how efficiently a vaccine could provoke an immune response inside the body, and the degree to which it provides protection from infection.
Other aspects of these studies assessed knowledge gaps, outreach challenges of routine immunisation programmes and vaccine reception among parents.
“Results from our studies have been well-accepted by the WHO,” says Dr Zaman.
Furthermore, adds Dr Zaman, icddr,b’s studies of OPVs could have wider policy implications. “These results are anticipated to guide the worldwide polio eradication agenda in choosing the optimal vaccination intervention in an appropriate setting,” he says.
icddr,b’s OPV studies are also important for other reasons. “It is also widely known that the OPVs do not perform well in the developing country setting but little was known about why,” says Dr Rashidul Haque, a senior scientist and head of the parasitology laboratory at icddr,b. Dr Haque is contributing to the international PROVIDE study which is examining the performance of OPVs in developing countries, including Bangladesh.
The PROVIDE study found that the OPVs underperformed in Bangladesh due to a condition known as environmental enteropathy (EE) which develops in children living in unsanitary conditions. EE is characterised by abnormalities in the structure and function of the gut. This affects how nutrients are absorbed from the gut, but it also appears to reduce the strength of immune responses generated by vaccines given orally.
Thanks to immunisation, the numbers of cases of polio have fallen dramatically around the world. However, although OPVs are safe and highly effective, they have one drawback. They are based on weakened versions of live poliovirus, which can replicate but do not cause disease. The vaccine virus can also be excreted by immunised children and passed on to others.
This transmission of vaccine virus is not normally a problem, but if immunisation levels are low in a population, the vaccine virus may circulate for long periods and mutate genetically. These are called ‘vaccine derived poliovirus’(VDPV). Eventually, VDPVs may turn into a harmful form that causes disease in unvaccinated children.
Disease caused by VDPV is very rare, with only around 500 cases reported to date worldwide, but it is considered a stumbling block on the path to polio eradication. In order to eliminate the odds of further VDPV circulation, the polio eradication agenda eventually aims to switch to a different type of vaccine – the inactivated polio vaccine (IPV), which contains ‘killed’ virus that cannot revert to a harmful form.
Photo: GAC | AMC © DFATD-MAECD/Nancy Durrell McKenna. CC BY-NC-ND 2.0
Meanwhile, OPVs will be gradually withdrawn. Among the three types of poliovirus, type 2 cases have not been reported since 1999, but most VDPVs arise from reactivation of the type 2 vaccine virus. This is one of the reasons why, from early 2016, the WHO has decided to phase out the trivalent OPVs (tOPVs), which worked against all three types, and instead switch to bivalent polio vaccines (bOPVs) that would work against type 1 and 3.
This measure will stop any chance of VDPV circulation from type 2 vaccine and safeguard children who are as yet unvaccinated. There is now only one month to go until every country in the world currently using OPV must withdraw the tOPV and replace it with bOPV.
However, some concerns remain. For example, what if there is a wild polio outbreak of the type 2 poliovirus after the vaccines are withdrawn? Although this is a remote possibility, icddr,b is carrying out research that could provide a solution. Dr Zaman is testing a potential new monovalent OPV (mOPV2) that is specific for the type 2 poliovirus. If there is an outbreak, results from this study will help the global polio eradication programme decide whether to deploy mOPV2 from the WHO stockpile.
It is hoped that outcomes from these studies will continue to feed the polio eradication agenda. “I feel delighted that scientists at icddr,b are making key contributions to what will be a landmark medical achievement of the 21st century,” says Professor John Clemens, executive director at icddr,b.
The polio eradication agenda envisages a world where poliovirus, once eradicated, will never have the opportunity to return. It was never been this closer to achieving the goal, but securing a polio-free world will certainly require concerted efforts.
