The total imported vaccine is enough to inoculate 300,000 horses, and comes amid reports that all thoroughbreds in Australia may yet be vaccinated.
Federal Agriculture Minister Peter McGauran, in announcing the vaccine purchase, said it did not mean an end to eradication efforts.
"Our priority remains on containing and eradicating this insidious disease from Australia, and every effort is being made in this regard," he said.
Mr McGauran said the decision to buy more vaccine came after close consultation with state and territory governments, and representatives of Australia's horse industries.
"Taking into account the need for booster shots, the 750,000 vaccines will make it possible to vaccinate some 300,000 horses, if need be, by the end of the year.
"The majority of the vaccines will be used in New South Wales and Queensland, which remain the only states with confirmed cases of EI. However, targeted vaccinations will take place in non-affected states and territories, as has been the case in Victoria and the ACT."
Mr McGauran noted there had been calls from both the West Australian and Tasmanian racing industries for vaccine to be made available even though they are EI free, but no request had been made by either State Government.
"To date, the focus has been on vaccinating high value horses, located in infected areas, as well as securing a buffer zone, to prevent the further spread of EI," Mr McGauran said.
"We are now in a position to move to the vaccination of competition and show horses, to get the industry back on its feet as soon as possible.
"The current restrictions on horse movements and competitions have had an enormous impact on thousands of Australians. From local pony clubs and agricultural shows, through to the Australian Olympic team's preparations, and racing and harness industries.
"It is important that horse activities and events can resume as quickly as possible, while maintaining our strategy of containment and eradication.
"I thank all horse owners for their patience, during what has been, and will continue to be testing times."
In badly affected New South Wales, 3000 doses of vaccine are being made available to the Equestrian Federation of Australia for the inoculation of EFA-registered horses in the purple and red zones.
The risk of infection transfer is increased when multiple vaccination teams visit a property, so the EFA teams will liaise with the Primary Industries department and will vaccinate all eligible horses when they visit non-infected properties.
As of yesterday, NSW had 4696 infected properties, 448 labelled "dangerous contact" and 456 official "suspect". A total of 5059 horses have been vaccinated in the buffer areas, with vaccination centres located at Mittagong, Gloucester, Dubbo, Wellington, Armidale, Forbes/Parkes, Mudgee, Temora, Woodenbong, Gunnedah, Scone and Tenterfield.
The vaccination buffer framework is now almost complete, the Primary Industries Department says.
Queensland reported a total of 1291 infected properties yesterday, within an area of 2766 sq km. The disease remains contained within the red zone.
In other news, Tasmanian authorities have praised horse owners involved in the recent flu scare in the state's north-west.
"The owners of the horses that were suspect have all been very helpful and, of course, each did exactly the right thing by reporting the sickness in their horses so quickly," a spokesman said.
"The organisers of the horse events at the Burnie show had a good biosecurity programme in place and it was their good record of entrants that enabled us to identify and contact the owners of all contact horses very quickly."