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[LAGOS] An outbreak of type 2 poliovirus in Nigeria could be curbed with a readily available vaccine, according to a study.

Type 2 poliovirus was eradicated in the wild in 1999. However, the virus has resurfaced from a weakened form used to make the oral polio vaccine. This 'vaccine virus' can mutate and is able to infect people in under-immunised populations.

Researchers studied 278 children paralysed by type 2 vaccine-derived poliovirus (VDPV) and compared them with those paralysed by type 1 and type 3 wild poliovirus (the virus encountered in nature as opposed to derived from a strain of poliovirus used to produce vaccine).

They say that the VDPV is as easily-transmitted and dangerous as the wild types.

The study also found that the commonly-used trivalent oral polio vaccine, which contains the three types of wild poliovirus, is highly effective in preventing potentially fatal paralysis from VDPV in children.

Emmanuel Abanida, one of the authors of the study and head of the country's National Primary Healthcare Development Agency (NPHDA), told SciDev.Net that the research confirms "that using trivalent vaccine is very effective in areas where we have transmission of this virus".

Abanida said VDPV is still being transmitted because of low coverage of immunisation in certain areas, where the mutated virus can still infect children who haven't had all three recommended doses of the vaccine.

"Despite the enormity of the work we invest in immunisation, we still have pockets of places were children are not being reached," he said. "And of course when that occurs, the immunisation in such area is reduced and thus we have cases of VDPV."

"It's a very good thing that there is now a scientific evidence to back this up [that the trivalent vaccine can help tackle the VDPV outbreaks]," said Oye Ibidapo-Obe, president of the Nigerian Academy of Sciences.

"The Federal Ministry of Health is doing quite well in massive campaigns of prevention to encourage our people to embrace polio immunisation that will prevent this kind of virus ... they are well equipped to tackle it."

The best way of rooting the virus out completely is to strengthen routine immunisation so as to prevent person-to-person transmission, said Emmanuel Odu, a director at the NPHDA. "I believe we are making a great deal of progress in eradicating wild polio virus and the VDPV," he said. "We are improving policies by doing operational research that will help improve our tackling of the disease."

Ahead of the new polio eradication deadline of 2013, the Global Polio Eradication Initiative reports that the best progress is currently seen in Nigeria, where case numbers have plummeted by more than 99 per cent, from 312 cases at this time last year, to only three in 2010.

The report appeared in New England Journal of Medicine last month (24 June).

Link to full article in New England Journal of Medicine

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