A study investigating the level of immunity New Zealanders have to pandemic influenza (H1N1) will get underway this month.

Blood samples will be taken from 2500 people to see who has been exposed to pandemic influenza and developed immunity to it.

This information will be used to establish how many people are still at risk of contracting the illness.

The study is being undertaken by Environmental Science and Research (ESR) on behalf of the Ministry of Health,

Director of Public Health, Dr Mark Jacobs, says the health sector needs to find out what proportion of the population has already developed immunity to the virus so it can plan more effectively for a possible second pandemic wave.

"We know that many people had a mild to moderate illness as a result of pandemic influenza this winter, but we need to get a clearer picture of the general level of immunity and how many people are still at risk. This is because the smaller the proportion of New Zealanders infected so far, the higher the chance of a significant second wave happening in the future.

"This is an important study. We hope people will agree to take part in it if they are asked to do so," says Dr Jacobs. "And people who take part will of course get to find out their own test result".

A two week pilot study is expected to begin within the next few days at a single practice in the Hutt Valley. It will be followed by a nationwide study that will run from later in November until March next year.

People randomly selected from participating general practices throughout the country will be asked to take part.

The final report is expected in May.