(Vox) – Once a leading killer of children, polio has nearly been wiped out by a global vaccination effort. Polio just got one step closer to becoming the second human disease to be fully wiped out. On Thursday, World Polio Day, the World Health Organization (WHO) announced that type 3 poliovirus has been eradicated worldwide.
For polio to be fully eradicated, all three wild polio strains — types 1, 2, and 3 — need to stop circulating. The three strains all cause the same horrible symptoms, including paralysis and death, but are virologically distinct.
Type 2 was eradicated back in 2015; the last case of type 3 polio surfaced in northern Nigeria in 2012 and the virus hasn’t been seen since. A poliovirus can be considered eradicated if it hasn’t been detected for three years.
Today, only type 1 remains at large — in Afghanistan and Pakistan. If it’s eradicated, polio will join smallpox as the only two human diseases wiped off the face of the planet. (A third disease that’s been eradicated, rinderpest, is spread mainly in cattle.) And today’s news is a step in that right direction.
The current goal for full polio eradication is 2023.
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