Australian researchers believe the flu virus is mutating, leading to fears that flu jabs will become less effective.
Australia is having one of its worst flu seasons on record with 220 deaths. Two people have died in New Zealand so far.
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"All of my children have had the flu shot, but funnily enough we still all got sick afterwards," said Penny, a Sydney mum-of-three.
Researchers may have discovered why, finding a monster strain of flu that has mutated - making the current vaccine less effective.
"If that's the case we are going to continue to see cases, particularly in the elderly as we move through the winter," says Professor Paul Van Buynder, an influenza expert from Griffith University.
It's believed the H3N2 strain of flu has contributed to one of Australia's worst flu seasons on record.
"The problem with influenza, like so many other viruses, is that it does mutate quite quickly," says Dr Kean Seng Lim from the Australian Medical Association.
"It's a little bit scary I guess, especially with young children, it makes you second-guess whether it's worth having the flu shot," says mum-of-three Penny.
More than 120,000 people in Australia have been struck down by the flu this season, and 220 have died. However, experts still say the vaccine will provide some protection.
Australia's worst flu season on record was in 2017, but this year already five times as many people have contracted the virus - and the height of the flu season is traditionally in September.
"That's why we keep on looking at different types of influenza vaccine, that will last better and have a better match," says Buynder.
It is hoped that the universal jab would last up to ten years, even a lifetime - but researchers say it is still a long way off.