I'll take the utilitarian route and just say "whatever you do, make it cause most good or, at least, least harm."
Lying is fine if it helps you and doesn't hurt others. Lying is not fine if it hurts others more than it helps you.
In the case of the vaccine, it doesn't stop you from contacting or spreading the disease, so the moral imperative to take it is basically nonexistent. It's all personal choice at that point. But if you're expected not to have harsh symptoms of the disease and you suddenly do have said symptoms, you're hurting your employer by having to take those days off so...
Lying is fine if it helps you and doesn't hurt others. Lying is not fine if it hurts others more than it helps you.
In the case of the vaccine, it doesn't stop you from contacting or spreading the disease, so the moral imperative to take it is basically nonexistent. It's all personal choice at that point. But if you're expected not to have harsh symptoms of the disease and you suddenly do have said symptoms, you're hurting your employer by having to take those days off so...