Nigeria struck by a polio epidemic caused by vaccination

[29 September 2007 - 10h58]

News of another hard blow to polio vaccination in Africa. The north of Nigeria has been hit by a new epidemic outbreak of polio. This is not due to the wild polio virus but to the emergency vaccination campaign under way to “make up for” the ground lost during recent years. However, in the light of this situation, which has occurred before, the WHO wants to reassure people.

The oral vaccine used in immunisation campaigns is produced from an attenuated virus but can nevertheless cause outbreaks of the disease of varying size. Familiar to specialists, this phenomenon can occur in areas where the immunisation rate is particularly low, as is the case in the north of Nigeria.

Precedents already exist. There have been nine of them in total over the last 10 years, leading to 200 cases of polio. However, during the same period, over 33,000 children worldwide were infected by the wild polio virus. And 6.5 million cases were prevented thanks to the vaccination.

These are the figures quoted by Sona Bari, spokeswoman for the WHO’s polio eradication initiative. She therefore stresses the importance of vaccination. “The risk for our children from the wild polio virus is so much higher than the risk associated with vaccination. The vaccine can cause paralysis but the risk is minimal. The outbreak (taking place in Nigeria) is larger than one might have imagined, it’s true. There are 69 cases, but we should not forget that at the same time Nigeria is facing 2,000 cases of polio as a result of the wild virus”.

The oral vaccine also gives indirect immunisation

Out in the field, the work of UN teams (from the WHO, UNICEF, etc) is proving difficult, although polio eradication did appear to be on course. The objective remains, now more than ever, to reassure people who are already suspicious of the oral polio vaccine (OPV) recommended by the WHO for the eradication of the disease.

An injectable vaccine exists which, according to Sanofi-Pasteur, would avoid the cases resulting from vaccination. But, as Sona Bari points out, “the oral form is the essential tool in eradication campaigns”. This is because the virus it contains – attenuated but still alive – multiplies in children’s bodies before being excreted in their stools. It therefore continues to live in the surrounding environment, thus infecting those around who, in this way, also gain protection. This is how children who have not been directly vaccinated themselves become spontaneously “immunised” by vaccine strains.

Source : WHO, Interview with Sona Bari, 28 September 2007, Sanofi Pasteur

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