A study investigating New Zealanders' level of immunity to swine flu starts this month.
Voluntary blood samples will be taken from 2500 people to see who has been exposed to pandemic influenza (H1N1) and developed immunity to it -- which will indicate how many people are still at risk of contracting the illness.
Director of Public Health Mark Jacobs said it was an important study, the information was needed so the health sector could plan more effectively for a possible second pandemic wave.
The total number of deaths attributed to swine flu in New Zealand remains at 19.
"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."
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 next March.
People randomly selected from participating general practices nationwide will be asked to take part.
The study is being undertaken by Environmental Science and Research and a final report is expected in May.
The ministry said that last week there was a slight rise in the number of New Zealanders seeing their doctor in relation to influenza-like illnesses.
Most people were seeking advice for sick babies and children aged under four.
Meanwhile, swine flu cases are continuing to increase in many northern hemisphere countries.
Mexico has reported more confirmed cases of pandemic influenza since September than during the epidemic earlier this year.
In Europe, high rates of influenza illness have been observed in Iceland, Ireland, Britain, Belgium, the Netherlands and Ukraine.
