I called 惠氏 and was told that the $700 one (4 shots) is good for life. The $300 for age 2 and above needs a booster every 5 years.
My b took the expensive one at month 12 and 14. We did not take all 4 shots as we did not bring him out much before age one.
I would rather give him life immunity than take a booster every 5 years, though the nurse said after age 6, people do not get booster as the body gets stronger.