Vaccines prevent illness but maybe not infection.

https://sg.news.yahoo.com/test-positive-being-vaccinated-why-200643383.html

Medical experts are starting to change their tunes now after some people get infected after vaccinations.

Like I said previously below, the main purpose of vaccination is not to overwhelm the healthcare system.

http://sg-stock.blogspot.com/2021/01/pfizers-vaccine-wont-protect-you-from.html