A fast-mutating strain of the flu is defying medical experts' efforts to stop it and has already killed at least 73 people in Australia this year.

Victorian Infectious Diseases Reference Laboratory figures showed that the number of notified laboratory-confirmed flu cases in Victoria for the year to July 2 was more than 90 per cent higher than those for the same period last year.

A young Bacchus Marsh dad who died on Father's Day was the latest victim of the most widespread flu epidemic in 15 years.

Ben Ihlow's death came as an eighth person died after a flu outbreak at an aged-care facility in Victoria with 14 more facilities reporting outbreaks at the weekend.