Trainers who had runners at Ayr last week were given good news by the British Horseracing Authority - with Newmarket-based Simon Crisford also revealing positive developments at his yard.
The fixture at the Scottish track last Wednesday was one of the meetings at which the yard of Donald McCain was in action.
Three cases of equine influenza identified at McCain's Cheshire base led to a six-day shutdown of racing and that figure subsequently rose to six - significantly including Raise A Spark, who ran at the Ayr fixture.
Trainers who saddled runners at Ayr had been unable to take part in the resumption while awaiting clearance, but can now have runners.
The BHA tweeted: "All 22 trainers who had runners at Ayr and were awaiting results are now cleared to run after a discussion between BHA and its vet committee.
"All horses who ran at Ayr returned negative tests and the majority of other horses from those yards were also tested & all found negative."
Four horses from Crisford's stable that had tested positive have now returned negative results, the trainer said.
The BHA announced on Sunday night that four cases had been identified in vaccinated thoroughbreds at Crisford's Kremlin House stable, meaning a stable other than McCain's had horses with the highly-infectious virus.
Now, much to Crisford's relief, the affected horses appear to be clear.
He tweeted: "Good News. All 4 horses who had previously tested positive for Flu have now returned negative results. Further testing to take place next week."