This year's flu vaccination has been beefed up following a particularly bad season in the northern hemisphere, but given the unpredictability of the virus it's still difficult to know exactly what strains will be circulating in the months ahead.

There were currently four seasonal influenza viruses circulating globally - influenza A(H1N1), influenza A(H3N2), influenza B/Yamagata lineage and influenza B/Victoria lineage.

The A(H3N2) strain had been included in New Zealand's vaccination this year, at the recommendation of the World Health Organisation, due to its association with an increase in hospitalisation and deaths in places such as Europe and the United Kingdom.

ESR strategic health intelligence manager Lisa Oakley said the vaccine had been changed from the northern hemisphere version to take into account the slightly different strains circulating in the southern hemisphere.

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"The flu virus is clever - it can change in itself very slowly year by year, or there can be big changes in the genetic material, which is when pandemics can occur."

While people spoke of developing an immune response to the flu, such changes meant that while someone may be protected from one strain having already been exposed to it, the immune system may not be able to recognise a new strain, and as such meant it was important to be vaccinated each year, she said.

"If you have had a vaccination in previous years you have some immunity to strains that were in it, but no immunity to what's coming in the new flu season."

She said that while being vaccinated was the best option to prevent getting a flu, other prevention measures such as basic hygiene - coughing and sneezing etiquette, hand washing, and staying at home when sick were also important.

To better track the flu and its severity, the ESR this year launched a new "dashboard", providing a near real-time measure of the impact of the flu through the season, and to help the health sector manage it.

While it was aimed at health professionals, it would also provide a guide to members of the public, Dr Oakley said.

"The new system will also be extremely useful in the event of a flu pandemic.

"Multiple flu viruses circulate in a season; some are worse than others, some parts of the community are more vulnerable, and in some years a flu virus is worse than previously experienced."

With this year's flu season just beginning, Dr Oakley said the up-to-date information provided on the ESR website would be of great value.