2 ms·
As the article says, the trivalent vaccine is a live, albeit weakened, virus and occasionally reverts to the original virus which means it occasionally causes a
by marcinzm 7y ago
As the article says, the trivalent vaccine is a live, albeit weakened, virus and occasionally reverts to the original virus which means it occasionally causes an outbreak. The whole point of phasing it out is to get rid of polio which you cannot do if the vaccine itself is causing outbreaks.