It's not a business unless you make yourself a guinea pig on a regular and ongoing basis for the purpose of making a profit.  Assuming that is not the case, this is "other income" and is not reported on a schedule C.

Turbotax changed the interview this year and then I think they made more changes after complaints, so I don't know exactly how to best address this.  There should be a series of test questions like "did you do similar work in the past or will you do similar work in the future?", "do you intend to earn money?", "is this similar to your main job?"  Answer all these questions as NO, to block the program counting this as income from working.

Also, there used to be a checkbox for "medical study" on a page of special circumstances, that should also take care of it.

If you have already created a schedule C by mistake, you will need to delete the 1099 and delete the schedule C before re-entering the 1099 as medical study income.  You can delete the schedule C from the Tax Tools menu, there is a selection for "remove a form". 

Thank you very much!  And no I don't plan on hiring myself out as medical guinea pig on a recurring basis, though I have had a request from some other lab that I politely declined.  🙂

For 2021 taxes, after choosing Research study subject, Tax asks if "you performed a service." Is getting a vaccine that is being tested and surviving and reporting that you survived performing a service? Or not? What is the definition of "performing a service" according to the IRS?

No, you did not perform a service and this is not like your regular job. Answering no to these questions will prevent a Schedule C from loading.