We've become used to looking out for symptoms like a runny nose, cough and fever as signs of a Covid-19 infection.
But now health authorities are warning people across the east coast to be on high alert for measles.
At least three cases of the highly infectious disease have been recorded at sites in Sydney, Melbourne, Brisbane and the ACT, likely brought to Australia from overseas.
Symptoms usually start as a fever, sore eyes and a cough, and then develop into a red, patchy rash that begins in the head and spreads through the body.