People who are immunocompromised or who have an autoimmune condition may get serious complications from vaccines. It is, in fact, a well known contraindication.

Some people do not know they are in one of those groups, and ARE likely to experience harm. These groups (unaware immune issues) are statistically insignificant compared to the entire population, of course.

But ignoring them is in fact contributing to the antivax movement; primes are statistically rare but if you told people they don’t exist, you would be working for the antimath movement.