The flu has hit elderly Cantabrians hard in the last month, with the highest hospitalisation rates from the virus since 2012.
But Canterbury Medical Officer of Health Alistair Humphrey said the situation could be even worse if not for the high number of people who had been vaccinated.
So far this year, 318 people have been hospitalised with the flu, including 182 last month alone.
In the same time last year, 226 had been hospitalised.
But the rates of flu-like symptoms reported in the community are lower this year than they were last year.
Last year, the flu vaccination was not effective, because it targeting a different strain of flu to the ones which proved most common.
Dr Humphrey said the type of flu being seen in Canterbury was different to the strains in other parts of the country.
"Had Canterbury not had such high rates of vaccination, it is likely that we would also have experienced high rates of infection from other influenza strains, like the rest of New Zealand," he said.
Canterbury had the highest vaccination rate in the country this year, with 176,690 vaccines distributed as of June.
Age Concern Canterbury chief executive Simon Templeton said a lot of older volunteers had to take time off over the past few weeks because they were down with the flu.
"We were actually talking about it only three weeks ago, saying it has been a quiet season, and then everyone seemed to come down with it at once," he said.
But he believed the vaccine was working.
"If younger people get vaccinated it is protection for the older people in our community," he said.