No benefit comes without a price: polio vaccine

http://www.reuters.com/article/2015/10/12/health-laos-polio-idUSL8N12C2NO20151012

The risk of vaccine-derived polio cases can be avoided by switching from using live oral polio vaccines (OPV) - which are highly effective, cheap, easy to deliver but contain live virus, - to "inactivated" vaccines (IPV), which are not effective for fighting endemic disease but contain no live virus.