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The following is an extract of Burnet Institute Deputy Director Professor Mike Toole’s commentary for The Conversation on the implications of recent cases of polio in Ukraine and Mali.
The World Health Organization recently reported two cases of polio in Ukraine and one case in a Guinean child in Mali. All three cases were identified as “vaccine-derived”, a mutant form of the original, “wild” poliovirus.
Polio is a highly contagious and devastating disease, which mainly affects young children in areas with poor sanitation. The virus invades the nervous system and can cause permanent, incurable paralysis or death. The recent outbreaks are a setback for a year that has otherwise produced some major achievements in polio reduction.
The number of cases caused by wild poliovirus dropped to 39 this year compared to 169 in the same period last year. At the end of July, Nigeria, which along with Pakistan and Afghanistan is one of only three countries that hadn’t eliminated polio, marked 12 months without a single case. In August, the entire African continent announced it had been polio-free for 12 months.
Among these great gains in polio reduction, news of three infected children is a significant reminder that no country can be complacent. Every child should be immunised against polio.
There have long been warnings that Ukraine’s under-immunised population was vulnerable to a polio outbreak. In June 2013, the medical journal The Lancet highlighted that only 50 percent of Ukraine’s children were fully immunised against polio, measles, rubella and other diseases - compared with 92 percent in Australia.
Ukraine’s low immunisation rates are partly due to the strong anti-vaccination lobby in the country. A UNICEF survey found that only 46 percent of Ukrainian parents had a positive attitude towards immunisation. But immunisation alone can protect children from the virus and prevent potentially permanent paralysis.
The most common polio vaccine used in the world is oral polio vaccine, which contains three types of live, weakened viruses. The vaccine induces immunity against all three types of wild poliovirus in the gut of a vaccinated child. This prevents the viruses from entering the bloodstream and the nervous system to cause paralysis – polio’s worst symptom.
But, in rare cases, the weakened virus in the oral vaccine can also cause paralysis. This is estimated to happen in one in nearly three million children receiving their first dose of oral polio vaccine. For this reason, most higher-income countries, such as Australia, have switched to the injectable, inactivated (or dead) polio vaccine, which induces immunity in the bloodstream and from which there is no risk of paralysis.
The outbreaks in the Ukraine and Mali are a timely reminder that all countries in the world need to maintain high polio immunisation rates. In an era when people travel with their children to all corners of the world, both the wild virus and the vaccine-virus can readily be imported and can infect and paralyse those children who are not protected, including the eight percent of Australian children who are not fully immunised.
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