Although OPV is safe and effective, in extremely rare cases (approx. 1 in every 2.7 million first doses of the vaccine) the live attenuated vaccine virus in OPV can cause paralysis. In some cases it is believed that this vaccine-associated paralytic polio (VAPP) may be triggered by immune deficiency. The extremely low risk of VAPP is well known and accepted by most public health programmes in the world because without OPV, hundreds of thousands of children would be crippled every year.
Polio is one horrible disease. As I was vaccinated as a kid, I had no problem changing my kiddos diapers. It was interesting at how long it took for (probably because it was rare as most HERE were vaccinated) cases to occur enough that it was put into the warning pamphlets and appear in Journals and Media articles.