Some possibilities:

One shot: Older adults currently aren't on the priority list to get swine flu vaccine but they should get the seasonal vaccine, which is already available.

Two shots: There's a potential for the regular vaccine in one arm and the swine flu vaccine in the other, if that one requires just one dose.

Three shots: The swine flu vaccine might require two doses three weeks apart, plus the regular vaccine.

Four shots: There's even this possibility for some children. Youngsters under 9 who are getting their first-ever regular flu vaccination need two doses of it.