"It usually takes something like that for people to get going."
A virus expert warns adults aged between 20-49 are particularly at risk of contracting flu this year.
Institute of Environmental Science and Research virologist Sue Huang said the last two weeks had seen an increase in winter flu rates and several strains of H1N1 virus - commonly known as swine flu - were prominent.
In the 2009 global swine flu pandemic, young children in particular were hit hard and have since developed better immunity to the H1N1 virus.
However young adults escaped the worst at the time and did not need to develop such high immunity levels, meaning they were now more susceptible to the virus.
"I would encourage young people to get more vaccinations," Dr Huang said.
Associate Health Minister Jo Goodhew said winter flu cases had not yet peaked.
"As the peak is still to come, hospitals are likely to see more people with the illness, so it is worthwhile to extend the funded vaccination season."
The seasonal influenza immunisation programme is free for people aged 65 years and over, pregnant women, people with long-term health conditions such as severe asthma, and children under 5 who have been hospitalised for a respiratory illness. For anyone else aged six months or older, the vaccine is available for a fee.
Those who are already unwell should seek advice from their doctor, nurse or Healthline (0800 611 116).
