A seat belt is not quite the same. Both sure involve autonomy. However, not wearing your seat belt mainly puts your self at risk. A virus can spread to others.
As for externalties of like medical care sure not using a seat belt or taking the vaccine mean your more likely to need medical care. I will add though without seat belt your more likely to die at the scene. Thusly, how much more externalties not wearing a seat belt will cause I don't know, and would need some data on that point.
There is also an other big difference between a seat belt and vaccine. Mandating a vaccine is forcing someone to under go a medical procedure. Albeit a simple one. Where as a seat belt does not.
Although, bringing up seat belts I find it funny we allow people to drive motor cycles on public roads, but you must wear a seat belt in a car. So clearly this was not just about externalties. So the rule seems quite silly to me. (probably the car insurance lobby pushed for it)
In my honest opinion it would be better the state did not mandate either of these in my opinion. What is sad is the vaccine some how has become political, and people are not taking for either stupid reasons or believing false hoods. Despite this I don't think we should be quick abandon principles of liberty because of idiots. Every precedent set today can be used to forward an other one in the future you may not agree with. So best tread carefully.