The vaccines are not 100% effective...but rather in the 90-ish% range. So you can still get COVID after being vaccinated...but for the most part, it'll be a mild case.
That being said, nobody under the age of 16 can currently be vaccinated (that could change next week to age 12), and the last time I checked, a significant number of guests of theme parks are under that age. So I'm good with keeping all preventive measures that work in place until the pandemic is much closer to being over. (And since thermometer checks are more theater than prevention, I'm fine with retiring that one...)