I don't think even a scientific study would be effective against odds as small as 450 out of 45 million. Vaccines are tested by hundreds, or thousands of people

I don't think even a scientific study would be effective against odds as small as 450 out of 45 million. Vaccines are tested by hundreds, or thousands of people before mass produced. Catching an event as unlikely as this doesn't seem possible. One would hope animal models would be helpful, but what if vaccine only causes GBS to humans?