KEY POINTS:
Fewer than half New Zealand's young children are thought to be still protected against the meningococcal disease epidemic, despite a $200 million mass vaccination campaign.
The vaccine injections give short-term immunity against the New Zealand B-strain of the bacteria.
But this drops below protective levels within months, says a report by the Immunisation Advisory Centre at Auckland University.
Only about 40 per cent of children aged six months to 17 months are now protected, the report says.
Health campaigner Lynda Williams said parents were not told how quickly the immunity wore off, leaving them with a dangerously false sense of security.
The vaccine injections were available to everyone under 20 between July 2004 and December 2006.
The programme ran until May this year for children under 5.
Originally three doses were given, but after it was found that babies' immune responses were much weaker than those of older children and teenagers, a fourth dose was added for babies at 10 months.
The advisory centre report, written in April, says that in the majority of young children given the injections, antibody levels against the bacteria were below the protective level by seven months after the third dose.
But immunity declined less rapidly in older children.
The centre's clinical director, Dr Nikki Turner, said yesterday the mass campaign was justified,"because we are talking about a reduction in disease and deaths in children ... "
Ms Williams, co-ordinator of the Maternity Services Consumer Council, criticised the absence of details on the rapid immunity decrease in fact sheets given to parents.
"It's information parents need so they don't think because their child has been vaccinated that a year later, if their child exhibits symptoms of meningococcal B, 'it can't be that', and delay seeking treatment, which could be fatal."
The Health Ministry's senior adviser on public health medicine, Dr Alison Roberts, said last night that Ms Williams' concerns were reasonable.
"But what we've always said to parents is that the meningococcal B vaccine would only prevent the epidemic strain, and they had to continue to be aware about meningococcal disease."
Dr Roberts said the question of duration of protection was complex.
Although blood antibody levels against the bacteria decreased rapidly after vaccination, there had not been a subsequent rise in the number of cases.
She said today's comparatively low number of cases indicated the vaccine had remained effective in most children, and that the bacteria were much less widely carried in the community than they had been.
Acting Health Minister Steve Chadwick said the vaccine acted as a "circuit breaker", preventing cases of the disease during an epidemic.
The campaign also raised awareness, probably resulting in quicker diagnosis and treatment.
"This has saved many people and their families from the horrible consequences of the disease such as death, disfigurement, brain damage, deafness, and life-long learning disabilities," she said.
"Is that money well spent? Ask anyone who has dealt with these consequences."
* War on epidemic
The Government has spent more than $200 million on the mass vaccination campaign against New Zealand's epidemic strain of meningococcal disease.
More than 1 million people have had the vaccine.
The epidemic, waning since 2001, began in 1991.
The peak year was 2001, in which 370 cases were reported. Last year there were 47.
Statisticians have calculated that in the two years after it started, the vaccination programme prevented 54 cases of disease and 1.7 deaths.
The vaccine gives only short-term protection.
