Parents should have been told more clearly that the vaccine against New Zealand's epidemic strain of meningococcal disease provided only short-term protection, says the head of the trials that led to its mass use.
Professor Diana Lennon, an Auckland University paediatrician, told the Herald yesterday that "it might have helped" to do this.
"I would have liked to have talked about it a bit more at the launch. I think it is a reasonable statement to say more discussion would have helped at the time because the truth will out, every time, and it's important," Professor Lennon said.
Her comments follow the Herald's report yesterday that medical experts had found the MeNZB vaccine given to more than a million under-20-year-olds in the Government's $200 million-plus campaign provided protection for a period of only months.
The mass programme began in 2004 and tapered to an end in May this year, although the injections are still available for infants' follow-up doses and for those at high risk of the disease.
Health campaigner Lynda Williams is concerned the lack of full information on the vaccine's protective duration may have lulled parents into a false sense of security about the killer disease.
Professor Lennon said most people who had been vaccinated would no longer be protected, apart from some of the older ones. Under-5s were the most vulnerable and few of them would still have protective antibodies.
"Unfortunately the vaccine does decay fast. That was always known from the literature and we confirmed it in our trials."
In a draft paper for a scientific journal, she and colleagues say: "MeNZB vaccination was not expected to provide long-term protection. In the youngest age group studied (6- to 8-month-old infants) only 27.5 per cent had ... antibody [levels] likely to protect, at 7 months after the third dose of vaccine."
But the Ministry of Health said leaflets given to parents, and to young adults considering having the vaccine, had stated: "The majority of people are expected to be protected but the vaccine may not protect every person who receives the three doses. Protection is expected to last for a few years but the exact period is unknown."
When asked if it had not stated the short duration of protection out of concern that it might undermine public confidence in the vaccine, the ministry repeated its statement, saying it remained valid "in the absence of a clear scientific answer".
It was the best estimate at the time, said the ministry's senior adviser on public health medicine, Dr Alison Roberts, and any updates were given to health workers as they became available.
The ministry said it had made a public statement in 2006 that explained the weaker immune response in babies and that for this reason a fourth dose would be offered for them.
Professor Lennon said it was unfair to judge the campaign with hindsight. It was not clear at the height of the epidemic, in 2000 and 2001, how long it would last without a vaccine.
The disease had virtually disappeared in Auckland, she said. Paediatrician Dr Teuila Percival, of Kidz First at Middlemore Hospital, said she had not seen any children with the epidemic strain since the vaccination campaign, compared with several a week at the epidemic's height.
* 109 cases of the epidemic strain of meningococcal disease have been reported involving people who were vaccinated, 60 partially and 49 fully.
* The most recent of these was a fully vaccinated child last month.
* The vaccine is estimated to have provided protection in 73 per cent of those fully vaccinated, but generally only for months, not years.
* The mass vaccination campaign achieved three-dose coverage for 80 per cent of the target group, those aged under 20.
* But just 50 to 60 per cent of babies had the fourth dose needed by this age group.