Minister looks at tests to fight swine flu

Tony Ryall. Photo / Mark Mitchell

Planning is under way for a blood testing programme by the Health Ministry to find out more about swine flu as Health Minister Tony Ryall warns that a second wave could be more severe.

In a speech to the National Health Emergency Management Forum, the minister said a serological prevalence survey - a series of targeted blood tests - was being considered to find out more about spread, levels of exposure and susceptibility in the population to H1N1.

"Probable cases" could increase again and a "future second wave of the pandemic may well prove to be more severe," Mr Ryall said.

"We don't know how many New Zealanders caught the virus in the first wave. Because it was mostly mild, many people cared for themselves at home while others may have been infected but had no obvious symptoms."

Officials estimate between 10 and 25 per cent of New Zealanders have been ill with swine flu.

At least 50 per cent of a population needs to be infected to provide sufficient community immunity.

Initial figures from Britain said as many as 30 per cent of a population could become ill, with the same amount experiencing only mild symptoms.

Information from the tests would aid future responses.

Deputy director of public health Darren Hunt said the wide variance of the estimates meant that health authorities understood only the "tip of the iceberg".

"We don't really know the proportion of the population who have been exposed, therefore we don't really know who might be susceptible to the virus in the future."

Issues such as who blood samples would be taken from and how many were needed were still to be worked through - a timeline hadn't been finalised but it was work that needed to happen soon, Mr Hunt said.

Much of the testing would focus on antibodies to the virus in the blood - how long they were in the body for, and what antibody levels said about immunity levels were questions which scientists would be looking to find answers for, Mr Hunt said.

But before that, tests had to be validated to make sure scientists were looking at the right antibodies.

A second wave of swine flu was a matter of when, not if, he said.

"Even though the flu level is declining, there's a lot of work going on because we know there's something to come - even if it's a month ahead, next winter or many years ahead. This is the opportunity to prepare for next time."