Trainers who had runners at those meetings have been asked to provide swabs of all horses in their yards for analysis.
The BHA added: "While no further positive tests have been received, at least three more days are required before it will be possible to make a decision about whether it is safe to resume racing".
The BHA warned yesterday that horses from the yard raced at Ayr and Ludlow on Wednesday, exposing other animals, including some from Irish yards to the risk of infection.
Horse flu is an "enzootic" disease, meaning it is native to animals, and in this case doesn't spread beyond horses and closely related species such as mules and donkeys.
Racing is still set to continue in Ireland, where Thursday's meeting at Thurles took place, but no entries from British stables will be accepted until further notice.
The BHA conceded "the full extent of potential exposure is unknown" but is working as fast as possible to gather information about any potential spread of the outbreak.
"Over the last two months, all potential runners have been scoped and their blood checked within 36 hours of their races to ensure that only healthy horses compete for the yard".
Wolverhampton is one of three racecourses doing a "deep clean" in the coming days.
More than 100 British racing yards have been put on lock-down by the BHA pending testing of all their horses, including those of Paul Nicholls, Nicky Henderson, Philip Hobbs, and Harry Fry.
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The outbreak was discussed in parliament on Thursday.
Cases of equine influenza had been reported in recent weeks, originally in France but spreading to Ireland and Britain.
The BHA said in a statement the identification of the virus in vaccinated horses presented a "cause for significant concern".
Horse racing across the United Kingdom has been banned today, Thursday, in a bid to stop the spread of a serious disease.
"The disease may be serious in unvaccinated horses, although symptoms in vaccinated horses are usually mild and transient". It is highly contagious.
In their latest statement, they said: "Humans are not at risk from the virus though can be transmitters of the virus".
A spokesperson for Defra said: "The disease is not notifiable in the United Kingdom and there's no public health risk".
The Jockey Club Estate's schooling grounds in Lambourn have been closed to outside horses as a precaution, a move which was reciprocated for Newmarket's gallops.