How are they infringing on others rights?
By knowingly making themselves an incubator for a communicable disease.
By their very nature, epidemics need to be managed at the society level. I think libertarianism is a fantastic base ideology, but communicable disease tends to not care much for individual-based thinking.
Really you're saying "you are going to have too many sick days, i can just tell it!" is justification for dismissal.
No, I'm saying, "You are going to make other people here, or their non-vaccinated dependents, sick."
I mean, this story is a perfect example that it isn't just a matter of sick days. Disneyland has a real nightmare on their hands.