Sad news today about vaccine-triggered polio outbreaks in Nigeria. The AP reports that this year, 124 children have been paralyzed by polio caused by mutated oral vaccine, up from 62 in all of 2008. Science magazine reported the news on 7 August, leading with the scary fact that the polio strain used to make the vaccine, type 2, had been declared eradicated in 1999 by the Global Polio Eradication Initiative. Now, due to the mutated vaccines, it’s “back from the dead”.

The news is particularly meaningful in Nigeria, which has had a prickly relationship with polio eradication campaigns. They suspended polio vaccinations in 2003, believing they were part of “the Western world’s plan to sterilize Africans or give them AIDS” (AP). They resumed vaccinations in 2004, and ”https://www.sciencemag.org/cgi/content/full/317/5846/1842">one year later the vaccine had mutated and began giving children polio.

Though such mutation was feared, it wasn’t wholly unexpected. “Experts have long believed epidemics unleashed by a vaccine’s mutated virus wouldn’t last since the vaccine only contains a weakened virus strain” (AP), but after it “limped along in characteristic [vaccine-derived poliovirus] fashion for a few years”, it took off in January 2009, Science says.

It’s a tricky situation. Nigeria uses an oral polio vaccine made from weakened but live polio virus, which can mutate. These vaccines are more practical than the vaccines used in Western countries, which are injected and made from killed virus and can’t mutate.

But switching to injected vaccines isn’t the perfect answer. Live vaccines are thought to be better for regions where the disease is still endemic because they activate an immune response in vaccinated individuals that causes them to excrete live polio virus particles. This passes along some immunity to those who come into contact with them. The WHO and US CDC officials say the oral vaccine is “the best available tool to eradicate polio” (AP) and that if vaccination rates were higher — near 100 percent — the outbreaks would be stopped.

Image: USAID.gov