Vaccines both cause and prevent diseases - Page 1

A new polio vaccine is being introduced worldwide .. the new vaccine reduces the number of polio strains in the polio vaccine from three to two types.  Type two polio has been eradicated ( the wild strain ) world wide and will no longer be included in the polio vaccine.  The reason given for the simultaneous world wide introduction of the new polio vaccine version is that those taking the previous three strain polio vaccine can infect those taking the new two strain vaccine with type two polio ( type two lab strain ).  As with most live vaccines those vaccinated can infect those unvaccinated and in some cases those vaccinated with another vaccine with fewer strains of the disease organism.

http://www.npr.org/sections/thetwo-way/2016/04/17/474580802/new-polio-vaccine-rolled-out-in-massive-synchronized-worldwide-switch