YOUNG children and the frail elderly should be vaccinated against the flu that has claimed the lives of three children in Western Australia.

The youngsters, under the age of five, died last week after suffering secondary bacterial infections on top of a common strain of flu.

Victorian health authorities have warned parents and carers to be alert to, but not alarmed by, the potentially deadly combinations of flu and bacterial infection.

But they have told carers to consider ensuring the most vulnerable in our community receive effective vaccination.

Three Perth children believed to have been suffering benign influenza A infection went on to develop secondary bacterial infection that became a deadly combination.

The conditions, neither seen as life-threatening on their own, can lead to full-blown pneumonia with disastrous results.

VHS spokesman Bram Alexander said Victoria had experienced fewer than half the number of influenza notifications this year than in the previous two years.

"We are down on numbers across the board and not even approaching our normal seasonal activity," Mr Alexander said.

"Our numbers are low with 63 notifications of influenza to date this year."

This compares with 115 notifications at the same time last year and more than 160 in 2005.

"But vaccination is a good thing and it works," Mr Alexander said.

"People with children or those caring for older people who are possibly more vulnerable should discuss with their own GP what course to follow."

Perth doctors complained last week that their state health authorities were too slow to warn of the possibility of a killer flu outbreak.

News of the deaths led to suburban surgeries being bombarded by parents anxious their children be checked out.

Queensland health chiefs yesterday called for young children to be vaccinated, particularly those suffering medical conditions such as heart disease or diabetes.

Flu symptoms mimic that of the common cold and can include fever, aches and pains, headache and fatigue.

Influenza is more serious than a cold and can cause diarrhoea and vomiting in children.