The event at Dunsborough scheduled for late in November is expected to attract up to 9000 people.
Based on advice from the state's chief health officers, anyone attending or working at the event will need to have had at least one vaccine dose by November 22.
The government said if there was a coronavirus case detected at the gathering, it would risk a serious community outbreak because of the lack of physical distancing, the mixing of non-family groups and the potential for poor contact tracing data.
"This is another sensible step to protect our young people at a big event but also the volunteers, workers and local community as well," Health Minister Roger Cook said.
"There is plenty of time for everyone wishing to attend the event to get vaccinated. Don't wait before it's too late."
The Dunsborough event is due to run from November 22 to 26.