Polio cases have nearly doubled this year in the West African nation of Nigeria as officials struggle to fight various natural strains of the virus as well as an outbreak set off by the polio vaccine itself three years ago.
Outbreaks linked to the vaccine, as opposed to the naturally occurring virus, are usually stamped out within months. But Nigeria has a very low immunization rate, partly from its weak health system and also from rumors about the safety of the vaccine.
Last year at this time, Nigeria had 54 reported cases caused by wild polio virus. This year, there were 106 new cases, according to figures released by the World Health Organization last week. The vaccine-sparked outbreak has struck more than 100 children so far, including eight this year.
For every paralyzed child, there are about 1,000 others infected and spreading the highly infectious and sometimes fatal disease, experts say.
"This is a huge step backwards," said Oyewale Tomori, a polio expert at Redeemer's University in Nigeria. He said the last time the country had every type of polio was in 1999 and described the current situation as "hugely traumatic."
Such outbreaks happen only when immunization rates are low.
Oral polio vaccine contains a weakened virus. In rare instances, as the virus passes through children who have not been immunized, it changes into a form dangerous enough to ignite new outbreaks.
An injectable polio vaccine is used in the West that does not cause outbreaks, but it is more expensive and must be given by a doctor or nurse.
"There are just way too many kids in Nigeria who haven't been vaccinated and that's allowing the virus to spread," said Dr. Bruce Aylward, director of WHO's polio department.
Nearly all the children paralyzed by polio are in northern Nigeria, where a yearlong boycott of the vaccine in 2003 triggered an explosion of the disease, which was exported to more than two dozen countries worldwide.
Hard-line Nigerian Islamic clerics called for the boycott, claiming an immunization campaign was part of a U.S.-led plot to render Muslims infertile or infect them with AIDS. The government finally reined in the boycott campaign, but up to 30 percent of children in the north have never had a single dose of vaccine, according to WHO.