The World Health Organization (WHO) recently confirmed the occurrence of two vaccine-derived polio cases in Ukraine and one case in Mali. The vaccine-derived polio cases are the ones caused by a mutant from the original wild poliovirus.

The circulating vaccine-derived poliovirus type 1, or cVDPV1, had affected children aged 4 years and 10 months in Ukraine, respectively. The dates of onset of paralysis among the children have been reported to be between June 30 and July 7, 2015.

The Guinean child in Bamako, Mali, has been affected by circulating vaccine-derived poliovirus type 2, or cVDPV2. The 19-month-old child's paralysis started one week prior to his arrival in Bamako for the medical treatment.

Although the number of reported cases of polio has significantly reduced globally, WHO believes that the incidence of three newly reported cases in Mali and Ukraine suggest why no country can be complacent about it and that every child should be immunized against the disease. Ukraine, on the other hand, has very low rates of polio immunization.

In June 2013, medical journal Lancet revealed that only 50 percent of the Ukrainian children are immunized against deadly diseases, including polio, rubella and measles, thanks to the anti-vaccination outlook within the country. A UNICEF survey claimed that only 46 percent of the citizens in Ukraine have a positive outlook toward immunization, thus putting the unimmunized children at a risk of contracting the deadly diseases.

The most common form of anti-polio vaccination provided to the children is the oral vaccine. The oral vaccine contains live, weakened virus that prevents the gut of the vaccinated child against all the types of wild poliovirus, thus preventing paralysis.

However, in rare cases, the weakened virus is also known to cause paralysis. It is estimated that the vaccine has caused paralysis in around 300 million children who received their first dose of immunization. Therefore, a number of high-income countries, including Australia, have switched to a new version of the injectable vaccine, which contains dead or inactivated polio virus. Such a vaccine protects the gut against the disease, however, does not result in paralysis.

In addition, the virus from the oral vaccine is excreted over a period of six to eight weeks The excreted virus replicates in the environment and during the process, sometimes gets genetically mutated. These mutated versions are called circulating vaccine-derived polioviruses, or cVDPV, and can cause paralysis. Under-immunized children are at a great risk of catching the virus circulating in the contaminated water and food. There are three types of cVDPVs identified so far.

WHO, therefore, has stressed on the importance of maintaining high immunization rates within the countries to stop such deadly outbreak of the polio virus.