A spike in measles cases has sparked new fears among medical experts that the measles vaccine may no longer be working.

A joint investigation from the Victorian Health Department and several Melbourne hospitals has found 13 Victorians contracted the disease in recent years despite already being vaccinated.

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It's raised concerns the virus has evolved.

Measles is a highly infectious viral disease, with an estimated 110,000 deaths worldwide in 2017, mostly in children under five.

The first symptoms are fever, tiredness, cough, runny nose, sore red eyes and feeling unwell.

A few days later a rash appears.

Confirmed cases

There have been 92 confirmed cases of measles in Australia so far in 2019.

In the US, health authorities are grappling with an outbreak.

Thirty-three new measles cases were recorded in the US last week, most of them in New York, federal health officials said on Monday.

The new cases brought the number of confirmed cases this year to 1,077, the worst US outbreak of the virus since 1992.

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Research by the Department of Health, the Doherty Institute and Royal Melbourne Hospital shows that, between 2014 and 2017, 13 Australians who had been vaccinated still contracted the virus.

Medical experts suggest a third vaccination may be necessary to keep people immune.

Loss of immunity fears

The Royal Melbourne Hospital’s Dr Katherine Gibney is an epidemiologist at the Doherty Institute and the Victorian Department of Health and Human Services.

She says because Australia has done such a good job at eliminating measles, people who have had only one vaccine aren’t getting a natural immunity boost as the disease isn’t circulating in the community.

“If you had been vaccinated and came into contact with someone with measles you might get a little natural boost in your antibody levels,” said Dr Gibney.

The research, published in the Clinical Infectious Diseases journal, showed a number of people who were hospitalised with the disease had been vaccinated at least once in the past, but their immunity had waned over time.

Chevron Right Icon 'This research has demonstrated some vaccinated people are getting measles.'

They had what is called secondary vaccine failure, meaning they had at least one dose of the vaccine and showed antibodies in their blood, but that protection waned and they contracted measles.

The symptoms weren’t considered ‘classic measles’ – patients weren’t reporting fever, cough and runny nose - but they did have a rash.

“Normally, if people have documented receiving two doses of measles vaccine we would be confident they won’t contract measles, but that’s getting greyer – this research has demonstrated some vaccinated people are getting measles,” Dr Gibney said.