At least a dozen people have been diagnosed with measles and three have been hospitalised as an outbreak of the infectious disease which began at the Orana Steiner School in Weston continues.
ACT chief health officer Paul Kelly said eight of the people who had fallen ill were Year 9 students from the school and four were ''community cases''.
Health authorities had asked Orana families to keep all unvaccinated students home from school to help prevent infection.
''The end of the school year will be helpful for stopping it circulating within the school community, but unfortunately when they go out on holidays they may well interact with other ... people ... around Australia and this is how this tends to spread further,'' Dr Kelly said.
''This is why we've asked people to stay at home, so hopefully it will burn out by the end of the school year.
''Anyone who's unvaccinated will most likely have been infected by then and we'll come to the end of the outbreak. But I expect there will be more cases [before then].''
Dr Kelly said the outbreak had been linked to a person who had travelled overseas.
''I think I'm right in saying there hasn't been a measles case which is endemic to Australia for a long time,'' he said.
There was only one reported case of measles in the ACT last year.
Health authorities were continuing to contact people who might have been in contact with measles patients.
Contacts who had not been vaccinated could be offered a vaccine or the normal human immunoglobulin.
Measles symptoms can include fever, tiredness, runny nose and a cough, followed by a rash which appears between two and seven days later.
Up to a third of people with measles develop complications, which could include ear infections, diarrhoea and pneumonia.
About one in 1000 people with measles develops encephalitis.
This reporter is on Twitter: @pjean01
