Deaths from influenza could reach historically high levels this year.

 Epidemiologist Michael Baker said data so far, including high hospitalisation rates, pointed to a likely big increase in the number of fatalities.

However, that would not be known for sure until the end of the year.

On average, influenza was responsible for about 500 deaths a year.

But that figure was not straightforward to arrive at, and relied on modelling.

That was because there could be multiple factors in a person's death which were not always recorded as the primary cause.

Baker said one example was that a person could die of a heart attack but the heart attack would never have happened if they had not had influenza.

Data such as the number of calls to healthline and the number of hospitalisations were used to show how much flu was circulating.

"A lot more people got infected and therefore we saw a lot more seriously ill people," Baker said

Because a certain proportion would died from the disease, there would likely be a bigger number this year, he said.

"It's speculation but it has been such a severe influenza season based on hospitalisations we're almost certainly going to be a the upper end of the historic range," he said.

Data from PHF Science showed hospitalisations from flu and flu-like illnesses had been in the "very high" category for weeks.

In Auckland they were at 10-year highs.

This years peak of people with severe acute respiratory infection from influenza was 9.5 out of 100,000. Last year's was 4.3.

Next time there was a big outbreak, Baker said he would like to see more communication from health authorities about the risks and what people could do to protect themselves.

But it was good to see the vaccine was free this year to the most at-risk groups, he said.

That undoubtedly helped more people survive, he said.

Flu hospitalisation rates had started to fall for the general population in the past fortnight.