Single measles, mumps and rubella vaccines have bad records
It has never been explained what component of the MMR made it dangerous. Neither has it been explained why giving the vaccines singly removed the danger that had been present in MMR. What needs to be understood is that the measles, mumps and rubella vaccines had bad records before they were combined into MMR.
Before the measles vaccine was introduced, it was extremely rare for an infant to contract this viral infection. However, after three decades of measles vaccinations, more than 25% of all cases occur in babies under one year.