Yeast Extract is okay because the yeast has been blown apart in the making of this product instead of using them to ferment it, no actual yeast is whole and is therefore no longer the bacterial yeast.
A good example would be fearing two little ants because they may form a colony on your land, and not purchasing any compost bags or sand because there may be ants in these products. So you come here and ask whether dead ant smash paste is okay to purchase.
The answer is yes because there’s really nothing left of the infectious kind, and anyone who tells you any different needs to study microbiology.
(This may be an old topic but it came up in google and I wanted to make a point)