What constitutes a "sincerely held" religious exemption to a vaccine mandate?

Sweeping new vaccine mandates could force millions of vaccine holdouts to become inoculated against COVID-19, but individuals with earnest religious beliefs or disabilities that interfere with inoculation may still be exempt from getting jabbed. 

It is new territory for many employers navigating the issue, given how risky a proposition it is to allow unvaccinated employees to mingle with, and possibly infect, colleagues in the workplace.  Many large corporations already require COVID-19 vaccination to keep employees safe from the virus, and must, under the Americans with Disabilities Act (ADA) and Title VII of the Civil Rights Act, offer exemptions to individuals with either a disability or "sincerely held" religious belief that prevents them from getting the vaccine.