The 2 doses are exactly the same. PA had a problem where the supply was running low to give second doses on schedule Too many first doses were given and none held in reserve to do #2. So, they have pushed the second doses out from 3 weeks to catch up. They said should all be on track within 2-3 weeks, but upposedly not a problem to delay even a couple months. I think 3 weeks is minimum. That was specifically for Maderna