Production sources at the two shows tell TMZ ... as of Tuesday, 'Wheel' and 'Jeopardy' will be shot without live audiences. As for how long this will last ... our sources say it all depends on the spread of the virus.

Our sources say there are 3 primary concerns ... one of which is exclusive to 'Jeopardy.' Alex Trebek, who is battling stage 4 pancreatic cancer, has a compromised immune system from chemotherapy and other treatments. We're told execs felt it was too risky to expose him to large audiences.

There are two other concerns ... most of the audience members for both 'Jeopardy' and 'Wheel' are older -- lots of folks in their 60s -- and they are the most vulnerable to contract the virus and not beat it.

The third factor is that a number of people who attend tapings are from out of town and such travel is risky, given the spread of the virus.