A Victorian child has died during an outbreak of influenza over the summer season, and now health authorities are urging people to get immunised.

The death of a Victorian child from the flu over the summer season is a reminder for everyone at risk to get immunised, state health authorities say.

It's unclear when and where the child died, but Deputy Chief Health Officer Brett Sutton said authorities are not releasing further details to protect the family's privacy.

"I really don't want to give any details of this child," he told reporters on Friday.

"Obviously for the family involved, this is absolutely tragic and I don't want to put at risk identifying this child."

Dr Sutton said all vulnerable people - including children under five, pregnant women, people over 65, and those with pre-existing medical conditions - should be vaccinated for influenza.

The deputy chief health officer said he did not know if the child had been vaccinated.

"It's a very tragic case, but it is rare," he said.

"It does nonetheless highlight that flu can be a really serious illness and the importance of vaccination."

Dr Sutton urges parents to watch for symptoms or illness that are more severe than an average cold.

"It's a much more severe illness with high fevers, muscle aches and pains, joint aches and pains, and people really feel too unwell to be able to go about their normal activities," he said.

Health authorities also reported two influenza outbreaks at Port Phillip Prison and Melbourne Remand Centre.

Dr Sutton said it's unclear why the more than 2800 confirmed cases of summer flu are significantly higher than the same time last year, but acknowledged the rise of international travel and influenza being picked up overseas.

"The particular strains that circulate year on year change and some of them are more transmissible," he said.

The health officer also said Victoria had a "relatively quiet year" in 2018, which could mean less immunity in people.

"That can play a role in people who pick up the flu this year, because they've got lowered immunity or they've got less immunity to the flu, because they weren't part of a big season last year."