Huh? Plenty of previous non-covid vaccines require more than two shots.

What? More than two doses is extremely common for vaccines. See e.g. https://www.cdc.gov/vaccines/schedules/hcp/imz/child-adolesc...

Infants have three or four doses for some of their vaccines.

Utter nonsense. A lot of vaccines need multiple shots -- independent of the duration of the protection.