You should take the vaccine to show your total obedience to the state and the revolution.
No he/she does not. So long as he has anti-bodies running around in body, not likely to die from extreme covid sickness.
However in some situations, such as boarding a cruise ship, there is a limited time between when boarding starts and the ship sails. And they must check in thousands of passengers in that limited time. They check your ID, register your credit card, issue you a cruise card, etc. Now we have the covid pandemic situation going around. A vaccination document check is quick. To perform an anti-body test is neither quick or inexpensive. So it makes practical sense to require vaccination documents.