You'll be up for review shortly, here is your list of 'healthy' substances as declared by the health minister. Deviating from this list is considered unhealthy and you shall be scheduled for gastric band surgery and excluded until that time. (yes I'm being deliberately extreme :p)
Do you see how using such a narrow lens could be unwise? How many boosters are you willing to tolerate to maintain your certificate, 2, 5, 10? How about we make them a monthly requirement, any issues?
The certificate does not stop you catching or spreading covid, but it will make you feel more 'safe' and better about yourself.