Six people have come down with measles after contact with an overseas visitor who attended two family events in Melbourne earlier this month.
The Department of Health and Human Services is asking people to watch for the signs and symptoms of the disease after the cases were diagnosed.
The visitor, who has since returned to Vietnam, attended an event at Mornington on May 4 and another at St Kilda on May 5.
Before returning overseas, the man visited sites in Moonee Ponds, North Melbourne, Coburg, Mount Waverley, Mornington, Williamstown and St Kilda.
Victoria's acting Chief Health Officer, Dr Angie Bone, said people planning travel overseas - where the disease is more prevalent in many countries - should determine their immunisation status and if needed contact their GP to get vaccinated. A free Measles, Mumps, Rubella vaccine is available.
The six people who have since contracted measles - five adults and an infant - have had community contact while in their infectious period, but before developing symptoms, in a number of suburbs including the CBD, Geelong, East Malvern, Chadstone, Noble Park, Hawthorn, Oakleigh, Mount Waverley, Fairfield, South Wharf, Armadale, Abbotsford, East Melbourne, Baxter, Frankston, Karingal and St Kilda Rd.
Dr Bone said anyone who was in these locations from early May onwards should watch for symptoms.
Dr Bone said 27 babies and toddlers who had contact with the infant at a childcare facility were today immunised at Monash Medical Centre with immunoglobulin to help prevent them developing the disease.
This is the biggest linked cluster of measles in Victoria since March last year, when nine people developed the illness in an outbreak connected with Melbourne Airport.
Another adult diagnosed with measles this week, who has been to Bendigo and Echuca, is not connected to the other cases but has been linked to a previous case who acquired measles overseas.
The cases take the number of measles cases diagnosed in Victoria so far this year to 22.
Measles is a highly infectious viral disease that can cause serious illness. Those most at risk of serious illness include very young children and adults, particularly those with weakened immune systems. People can develop pneumonia and other serious complications from the disease, and often need to be hospitalised.
The illness usually begins with common cold symptoms such as runny nose, red eyes and a cough, followed by fever and rash.
"The characteristic measles rash usually begins 3-7 days after the first symptoms, generally starting on the face and then spreading to the rest of the body," Dr Bone said.
"Anyone developing symptoms is advised to ring ahead to their general practitioner or hospital first and tell them that they may have measles so that appropriate steps can be taken to avoid contact with other patients. If you think you might have measles, it's a good idea to stay away from other people as much as possible, particularly those who are unvaccinated or most at risk of serious illness, until you have been assessed by a doctor."
Anyone who is unvaccinated is at highest risk of contracting measles. The disease is now uncommon in Australia because of the widespread use of the measles vaccine, but the disease more is more prevalent in many countries overseas. Most cases of measles in Victoria have been linked to international travel.
The latest figures from the Australian Immunisation Register show that 95.7 per cent of Victorian five-year-olds are now fully immunised.
The measles vaccine is currently recommended on the National Immunisation Program at 12 months and again at 18 months. Immunisation is the best protection against measles.
People need to have received two doses of measles-containing vaccine to be fully protected. Many adults have only received one vaccine against measles and therefore most cases are in this age group.
Most people born before 1966 will have been exposed to measles in childhood, and therefore will be protected.
"This means if you are an adult born in or after 1966 - especially if you are planning travel overseas - you may be susceptible and should contact your GP to get vaccinated - and a free Measles, Mumps, Rubella vaccine is available," Dr Bone said.
Further information about measles can be found at the Better Health .