Australian health authorities are warning people in New South Wales, the A-C-T, Queensland, and Victoria to be on high alert for measles.
At least five cases of measles. - the highly infectious disease have been recorded at sites in Sydney, Melbourne, Brisbane and Canberra, likely brought to Australia from overseas.
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She says measles one of the most infectious communicable diseases that exists.
Dr Selvey also says it's "very clever" to pick out the one or two people in a big crowd who aren't immune.
While Australia is generally protected by very high vaccination rates - over 95 per cent - there are always people in the community who can't be vaccinated.
Dr Selvey explains those at risk include people who are immuno-compromised or have another kind of health condition, and very young children.
The World Health Organisation ((WHO)) has issued a warning about its spread after the number of annual cases in Europe jumped from 941 to 42,200 in just 12 months.
In Australia, the joint measles-mumps-rubella vaccine is given in two doses, and is free to anyone born after 1966.
That's because people born before 1966 are understood to have natural immunity, through childhood exposure before the vaccine was developed.
The success of that vaccination program, Dr Gibney explains, led to the World Health Organisation declaring Australia "measles-free" in 2014.
Dr Nicole Higgins is the President of the Royal Australian College of General Practitioners.
She says it's imperative everyone makes sure they've had both doses - and explains what to do if you're not sure about your vaccination status.
Dr Higgins recommends that people unsure about their vaccination history - or worried that they're showing symptoms - should visit their G-P.
But, if you think you have measles, she warns it's important to ring ahead, so that the G-P can take precautions at the clinic to avoid spreading this incredibly contagious disease.
