Exposure to the whole virus also produces a bunch of immune disregulating components which help make this virus particularly nasty. People get vaccinated to pr

Exposure to the whole virus also produces a bunch of immune disregulating components which help make this virus particularly nasty. People get vaccinated to protect themselves and others around them - boosters will increase that protection. Proof of vaccination is about excluding those who haven't been vaccinated - it is they who are on the train, though they can get off it anytime they choose.