The phrase “may be effective” lowers the standards for scientific evidence sometimes required for FDA approvals. Besides the presently licensed COVID-19 vaccines, the only vaccine that has been licensed underneath an EUA up to now was an anthrax vaccine in 2005. This vaccine was given to certain military personnel who had been at heightened risk of publicity to anthrax. If you develop COVID-19 symptoms at any time, you should isolate and get tested for COVID-19. You ought to isolate and get tested even if you are absolutely up to date along with your COVID-19 vaccines.