KEY POINTS:
New Zealand has spent more than $200 million on vaccinating young people against an epidemic disease that had already started waning. With the benefit of hindsight it is a decision that is easy to criticise, but at the height of the epidemic in 2001, when 370 cases were
notified and 18 people died, it seemed like a life-saving idea.
What is meningococcal disease?
It is a bacterial infection that can cause meningitis and blood poisoning. It can be spread by coughing, kissing and sharing a cup and in severe cases can lead to brain damage, limb amputations and death.
A number of strains exist, but the one causing New Zealand's epidemic is a particular B-strain organism.
How serious was the epidemic?
It began in 1991, peaking a decade later; the number of cases has declined annually since.
The epidemic strain killed 18 people in 2001 and a further 32 by the end of last year.
The population rate for all meningococcal disease was about 1.5 per 100,000 in the late 1980s, peaked at 17.5, and dropped to 2.6 last year.
But those figures conceal the fact that it is a disease primarily of poverty, minority ethnicity and early childhood.
In 2001, the epidemic strain alone afflicted the Pacific population aged under 5 with a rate of nearly 180 per 100,000 and the same age group among Maori at more than 110 - but both were down to around 20 per 100,000 last year.
Why did the Government spend so heavily on a mass-vaccination campaign?
In the late 1990s and early 2000s when the epidemic was rising, this seemed like the only option. Solving poverty and overcrowding did not seem feasible and encouraging people to seek early treatment for a disease whose symptoms could mimic the flu would only ever achieve limited success.
With the help of the World Health Organisation, the Ministry of Health made contact with the developers of vaccines that could be modified to target New Zealand's strain. The Norwegian Institute of Public Health's vaccine was selected and the Chiron Corporation was contracted to produce it for New Zealand use.
The "MeNZB" vaccine injections were given in schools and general practices from July 2004, ultimately to more than a million people aged under 20.
Did it work?
A statistical analysis has calculated that in the two years after the vaccination campaign started, it prevented 54 cases of disease and 1.7 deaths.
The epidemic is now considered largely to be over. Vaccine sceptics say it was on the way out anyway.
Vaccine supporters say MeNZB helped it go. Some add if the Ministry of Health had acted more quickly in the 1990s and the mass vaccination had begun sooner, it would have prevented more cases. But they also say focusing on the 54 cases in the analysis ignores the huge benefits for minority groups and those in poor areas.
How long does the vaccine effect last?
The answer varies. Levels of protective antibodies in the blood system after vaccination last only months not years, longer in adults than in babies.
Babies were offered a fourth dose because only 27.5 per cent had a protective level of antibodies at seven months after their third shot. However, little more than half of those entitled to the fourth injection actually had it.
Even after antibodies have dropped below the expected protective level, the immune system of a vaccine recipient would recognise the bug and start producing new antibodies, but probably not quickly enough to protect the person against large amounts of the bacteria.
There are now concerns that parents may have been lulled into a false sense of security by the lack of detail given to them over the brevity of immediate protection.
The ministry says it clearly told people they needed to be vigilant for disease symptoms even if vaccinated because the vaccine covered only one strain and did not work in everyone; and that protection was expected to last only a few years although the exact period was unknown.
Where to now?
The vaccine was originally intended for ongoing delivery to young children, but in May began to be withdrawn from routine use. This was mainly because its short protective duration had become more widely understood, the low uptake of the fourth dose and the comparatively low incidence of disease.
But supplies of the vaccine are being held in case the programme needs to be reactivated.