Normally, vaccines have a 10+ years of testing in order to check all the things people are worried about, such as still being able to infect others, unexpected side effects, conflicts with other medications and how long the protection lasts. But (almost everyone) agrees that the problem is so great that proceeding now is the least worst option.
With some 1.5 million dead already and countless people now with life-long health complications that are not yet understood, people can decide to stay home or get vaccinated.