The World Health Organization (WHO) has admitted that a new polio outbreak in Sudan is linked to an epidmic sparked by the oral vaccine.
News of the outbreak comes a week after the UN health agency declared that wild polio had been eradicated in Africa.
The WHO is now warning that there is a high risk of the vaccine-derived polio spreading across central Africa and the Horn of Africa.
Afghanistan and Pakistan are also struggling to contain outbreaks of the vaccine-derived polio.
The Guardian reports: In a statement on the new cases, the WHO said two children in Sudan, one from South Darfur state and the other from Gadarif state, close to the border with Ethiopia and Eritrea, were paralysed in March and April. Both had been recently vaccinated against polio.
The WHO said initial outbreak investigations showed the cases were linked to a continuing vaccine-derived outbreak in Chad that was first detected last year and is now spreading in Chad and Cameroon.
While so-called vaccine-derived polio is a known risk, the emergence of these cases so soon after the announced eradication of wild polio in Africa is a setback.
At issue is the fact that the oral polio vaccine – preferred in some places because of its ease of delivery and the lack of need for sterile syringes – uses an attenuated or weakened version of polio.
When a child receives the oral vaccine, the weakened virus replicates in the intestine, encouraging the production of antibodies, and can be present in excreta. In an area where there are high enough levels of immunity in the population, this usually does not present a problem, even if sanitation is poor.
But in areas where there is both poor sanitation and a lack of general immunisation the virus can survive and circulate for months, mutating over time until it poses the same risk of paralysis-causing disease as wild polio.
Use of the oral polio vaccine was discontinued in the UK in 2004 and the US in 2000, and the UN agency advises that the use of the oral vaccine should be discontinued after polio is judged to be eradicated because of the risk of vaccine-derived outbreaks.
