Polio, the dreaded paralyzing disease stamped out in the industrialized world, is spreading in Nigeria. And health officials say that in some cases, it’s caused by the vaccine used to fight it.

In July, the World Health Organization issued a warning that this vaccine-spread virus might extend beyond Africa. So far, 124 Nigerian children have been paralyzed this year, about twice those afflicted in 2008.

The polio problem is the latest challenge to global health authorities who are fighting myths that have abounded about vaccines: that they were part of a plan to sterilize Africans or give them AIDS.

Nigeria and most other poor nations use an oral polio vaccine because it’s cheaper and easier and protects entire communities.

But it is made from a live polio virus — albeit weakened — which carries a small risk of causing polio for every million or so doses given. In even rarer instances, the virus in the vaccine can mutate into a deadlier version.

The vaccine used in the United States and other Western nations is given in shots, which use a killed virus that cannot cause polio.

So when WHO officials discovered that a polio outbreak in Nigeria was sparked by the vaccine itself, they assumed that it would be easier to stop than a natural “wild” virus. They were wrong.

In 2007, health experts reported that amid Nigeria’s outbreak of wild polio viruses, 69 children had also been paralyzed in a new outbreak caused by mutation.

It is a worrying development for officials who hope to end polio epidemics in India and Africa by this year.