Ministry of Health officials are disputing claims that the hotly debated Menz-B vaccine does not provide the level of protection promised.
Officials told Parliament's Health Select Committee on Wednesday that claims about a drop off in protection are technically correct, but misleading.
The $200 million Menz-B vaccination campaign was rolled out between July 2004 and December 2006 to everyone up to the age of 20.
Since then, a new report has indicated that the vaccine gives short term immunity only, and that seven months after their third injection fewer than half the children had low and anti-body or protection levels.
The Health Ministry said on Wednesday that vaccinated children remain protected, even if they have low anti-body levels because their bodies remember and could still recognise the bacteria.
Health officials insisted that the campaign had been stunningly successful in fighting the meningoccoccal disease epidemic and said parents had not been misled in the information given to them.