There are now close to 1000 infected properties in New South Wales and Queensland, with up to 9000 horses affected.
Authorities say the spread of the highly contagious disease remains within containment zones, with most spread being property to property.
Officials says the number of cases may yet double, particularly in containment areas with a high horse population. The outer areas of Sydney, with a dense equine population, are seen as particularly difficult.
Buffer areas are being planned around restricted zones, with the possible use of vaccination to prevent the spread beyond affected areas. However, no approval has yet been given.
However, while calls grow for a vaccination programme to be introduced, a committee that has investigated the issues warns there is no quick fix, and that use of vaccine will likely prolong the need for control measures.
Australia's Consultative Committee on Emergency Animal Diseases, in a just-released report, said the question is complex.
"There are many issues that need to be considered," it stressed.
Vaccination can prevent disease, reduce the susceptibility of at-risk horses, and reduce farm-to-farm spread, the committee said.
"Apart from horse movements to New Zealand, there are unlikely to be any international implications of vaccinating."
However, the committee said, there were several clear disadvantages.
"Vaccination may mask clinical signs so vaccinated horses will need to be identified and monitored for evidence of infection."
There was a risk that a vaccinated horses that had the infection but was not showing symptoms could be moved to a new area, spreading the infection.
"Vaccination may prolong the need for movement restrictions because it may slow the transmission and spread of infection within areas. Vaccinating selected regions will lead to the country being separated into free and vaccinated areas. This will result in differential movement requirements and the need for infrastructure (permits, border controls, etc) to maintain the integrity of free areas."
It may require registration and passports for all horses.
"Vaccination is not an immediate option. It will take time to import vaccine (the permit process), deploy vaccine and train vaccinators, vaccinate the population and for immunity to develop.
"Vaccination may affect performance in the short term."
Vaccine use is likely to extend the duration of the outbreak and delay the ability to declare freedom, the committee said.
In other news, Thoroughbred Breeders Australia is seeking a special zone in the breeding heartland of the Hunter Valley, which would allow mares to be transported into the area's studs, where they would remain after being served. Mares within the zone could also be allowed to be moved between studs.
A Queensland apprentice has been barred from riding and ordered to appear before a stewards inquiry for an alleged breach of biosecurity requirements at Eagle Farm. The rider turned up with a skull cap and riding vest he used in Sydney at the in-house Warwick Farm meeting a week earlier.