What I remember but cannot currently find a source for, is that there are three levels of protection that vaccines can provide. First is to protect patients fro

What I remember but cannot currently find a source for, is that there are three levels of protection that vaccines can provide. First is to protect patients from developing the sickness (but not from being infected!), second is to even prevent them from spreading it and best outcome is to prevent them getting infected at all. Only the second and third level prevent spread.