It happened to us (Grimsby) earlier in the season. Three games postponed, albeit on the basis of a single positive test for a young pro who had been out on loan but continued to train with the first team, which seems daft in hindsight.
That clearly hasn't been the reaction to other isolated positive cases at other clubs - as far as I can tell there doesn't seem to be a consistent protocol to follow. It's going to interesting if we have a bad winter weather-wise, particularly in the lower divisions - fixture congestion unlike anything we've ever known.