A review of the government's $200 million meningococcal vaccination programme has found that the vaccine's effectiveness often wore off within just months of the injection.
The vaccination programme was developed especially for New Zealand children, and the review has found that nearly 50 percent of babies were not protected after the usual course of three injections.
Even after a fourth dose, one-in-four were still vulnerable to the disease.
Immunisation experts knew it would not work for some children, but did not realise how large that number was and incorrectly told parents that most children would be protected for a few years.
"There are many people out there who assumed that vaccines are going to last for a lifetime and are going to protect our children 100 percent of the time," Dr Vikki Turner says. "Sadly that's not true. We know this vaccine has been effective and has made a difference to disease reduction, but it's not a protective bullet for life."
More than a million children like Henry have received the vaccine and even though it has been effective in curbing the epidemic, its effect can wear off within months.
But despite its flaws, doctors say it did its job
"Back in 2001 we had 690 cases of meningococcal disease in New Zealand, with almost 400 cases of the epidemic disease," Dr Alison Roberts says. "We have had very few this year - only ten cases."
Parents say they would still have gone ahead with the vaccine anyway, as any protection is better than none at all.
3 News