This has been a big question here as we have just changed the age guidelines for the AZ (a couple of days ago). Strong advice here is go with the first dose. The medical officials say that the idea of mixing doses is “interesting” but there are no clinical studies available. Some very recent work suggests that the reaction to the different jab is higher but you won’t grow a second or third head and no ones arm fell off. No news yet on how well it provides protection but that work could be published “soon”.
My advice would be go with the same dose unless you speak with your medical professional first. I am booked in for my second AZ on Saturday.
Ask your doc, get the right jab for you, hug your grandkids