A baby boy too young to be vaccinated is one of three confirmed cases of measles in Melbourne with concerns the outbreak could spread.
A Melbourne woman unrelated to the infant, and a man who contracted the disease in Romania, have also been confirmed as having measles, the Victorian Department of Health announced on Tuesday.
"Measles is not a nothing disease by any means; one in three kids will get hospitalised with measles, sometimes with pneumonia, and it still kills people," Victoria's deputy chief health officer Brett Sutton said.
People who are unvaccinated, not up to date with their vaccinations and those too young to be vaccinated are at the greatest risk of contracting the illness, Dr Sutton added.
"If they've come down with measles, there's a reasonable guess they were under-immunised," he said of the three cases.
The woman and baby were infectious with the highly contagious disease between between September 6 and September 13.
While infectious they visited train stations between Armadale and Southern Cross, and visited Collins Street in Melbourne, Chadstone shopping centre, IKEA at Richmond and Ballarat.
The baby, aged under 12 months, and the woman had not been together, but could have come into contact with the same unidentified infectious source, Mr Sutton said.
The man who was confirmed as having measles on Monday was infectious while in transit on September 12, when he flew on Qatar Airways QR222 from Bucharest to Doha and on QR904 from Doha to Melbourne the next day.
The woman and man are both stable in hospital and the boy is recovering at home, authorities said.
The three infections take to 12 the number of measles cases in Victoria in 2017.