LONDON -- Horse racing has been canceled in Britain until Wednesday Feb. 13. at the earliest, due to an equine flu outbreak.
The British Horseracing Authority said it was informed Wednesday night by the Animal Health Trust of three confirmed flu cases from vaccinated horses in an active racing yard.
They raced on Wednesday and the BHA says they potentially exposed the flu to a "significant number of horses from yards'' in Britain and Ireland.
Racing had been due to take place on Thursday at several tracks, with more races planned for the weekend.
The BHA initially said: "The fact that the cases have been identified in vaccinated horses presents a cause for significant concern over welfare and the potential spread of the disease and the action to cancel racing has been viewed as necessary in order to restrict, as far as possible, the risk of further spread of the disease."
In an update on Thursday, the BHA explained that they were "assessing the scale and severity of the outbreak". After receiving test results, they released a statement saying that more than 50 trainers and veterinarians had been contacted to determine the risk of the flu spreading.
"Whilst 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," read the statement.
The authority added that a "fully informed" decision is likely to be made on Monday, allowing declarations to take place on Tuesday in time for racing on Wednesday.
The BHA have responded to public concerns by providing a Q&A on equine influenza, which can be read here.
Information from The Associated Press was used in this report.