Under recently announced changes that take effect on January 14, movement regulations have been tightened and all horse events have to be registered with the Department of Primary Industries.
NSW deputy chief veterinary officer Ian Roth said a concentrated effort was going into restoring disease-free status in the area around Sydney, the Hunter Valley and Tamworth.
"With about 84% of the state now in the green zone and no new infected properties since early December, it is clear that we are making real progress towards our goal of eradicating equine influenza from NSW," he said.
"The purple zone is a special restricted area where free movements were permitted due to the very high presence of the disease in the area at the beginning of the programme in early September.
"Our surveillance testing and investigations indicate there is little disease left and now it's time to tighten the movement restrictions so that we can identify any new outbreaks if they occur.
"These new restrictions will allow us to closely monitor movements and track any spread of the disease, so that we have the capacity to respond quickly to new infections before they go any further.
"However, movements outside of the zone are only allowed under permit, and strict conditions apply."
He said any new infected property will be quarantined for up to 50 days, and detailed investigation and tracing will be undertaken.
Meanwhile, veterinary teams will continue their surveillance testing and investigations throughout the area to identify remaining infected properties and map those that are free of disease.
Mr Roth said the changes bring movement restrictions in line with those that apply to the green zone where the THS has been very well accepted by other horse owners.
"This means a THS is required for each and every horse movement within the purple zone, other than those within a single property. The form must be carried with you on the journey," he said.
NSW DPI has developed a simple, self-issuing system to make it easier for people to obtain a THS, which involves logging onto the DPI's website at www.dpi.nsw.gov.au/equine-influenza.
People without internet access can phone the disease hotline on 1800 675 888 and have the approved form sent out to them (by fax or mail).
Horse events can also be registered on the website, or alternatively through the disease hotline.