Fine, prove that statement holds up in regards to Covid. Does one choosing not get vaccinated only effect them?Don't need to.
"my body, my choice" is a compelling argument, even if it would be more desirable for them to be vaccinated.
Similarly if you really care you can go look at the list of unpleasant side effects. If they tip their risk-reward calculations into such scenarios, despite the miniscule practical risk, it is still ultimately something society generally says is their choice.
The side effects of the vaccines have been shown to be temporary. Discomfort for a few hours to maybe a few days does not compare to the possible weeks to even lifetime side effects of Covid. Choosing to avoid a short period of discomfort with the risk of harming others goes beyond just one’s body.