The oral polio vaccine has a small chance of paralyzing or killing people it's administered to, around one in a million if I remember right - this may sound har

The oral polio vaccine has a small chance of paralyzing or killing people it's administered to, around one in a million if I remember right - this may sound harmless enough but polio's so rare that for a while it was a bigger cause of paralysis than actual wild polio infections, which is why everyone would like to eradicate polio and stop administering it and why developed countries now use the inactivated vaccine. It also has a small chance of mutating over time if it spreads through the community into a non-attenuated form which is much more virulent and carries a much higher risk of paralysis and death, and this has stymied attempts to eliminate polio and stop vaccinating.