Yes they were all written to and reminded on the 18th January. The BHA did so because of the concerns that this particular strain of equine flu which was evident elsewhere in Europe could get into the UK horse population.
Where they can't run it's definitely self-inflicted, but they still moan and complain. The owners have every right to be unhappy at their trainers who are fully responsible to make sure jabs are up to date at all times. Some horses could now miss intended preps and/or won't get marks to get into Festival handicaps.