WHILE Australia is one of 10 countries to declare itself measles-free, the confirmed case of the virus in the ACT in December revealed a small weakness in the nation's measles vaccination program.
Those aged between 20 and 40 are the most susceptible to measles among vaccinated Australians.
The latest case involved a vaccinated ACT woman in her 30s who was exposed to the virus via an overseas visitor to a Sydney dance party.
Having missed out on natural immunity through exposure to the virus - an immunity most older Australians have - younger adults are likely to have received only a single dose of the vaccine, which is now routinely administered twice.
"The measles vaccine was first introduced in the late '60s … and it was just one dose," said ACT Chief Health Officer Dr Paul Kelly.
"With the one dose immunity does tend to wane over time - it becomes a bit less effective and that is less likely to happen with the two-dose schedule.''
He said the single dose started with immunity for about 95 per cent of people; but combined with a vaccination rate of only about 80 per cent at the time, there was still an outbreak every year or two during the subsequent decades.
"If we give a second dose, it boosts the immunity to about 99 per cent," Dr Kelly said.
The second dose on the childhood vaccination schedule was introduced in the early 1990s.
"So those who are under the age of 20 are fine, but it's the 20 to 40-year-olds where we put this pretty constant message out, particularly if you're travelling overseas to places where measles might be more common - generally the poorer countries and the UK,'' he said.
''We advise people in that age group to have the vaccination before they travel."
ACT Health is now confident the one local case has not spread further and credited the territory's high vaccination rates against the disease, which can "spread like wildfire" in unvaccinated and unexposed populations, where an average single case will infect 15 others and spread from there.