KEY POINTS:
People who have been vaccinated against New Zealand's epidemic strain of meningococcal disease will retain a "memory" of it in their immune system, even though the associated antibodies will have dropped below the protective level, a leading scientist says.
Dr Diana Martin, who was closely involved with the 2004-06 mass vaccination scheme, said yesterday that "memory cells" in the immune system started producing antibodies again if exposed to the bacteria.
"The problem is that these memory cells don't immediately kick in such that in two hours you will have circulating antibodies again. It does take the immune system a few days [studies have indicated about four days] for them to make enough antibodies again to protect you," said Dr Martin, principal scientist at the Institute of Environmental Science & Research.
The new antibodies would either protect the person fully or leave them with an infection milder than it would otherwise have been.
But Auckland University paediatrician Professor Diana Lennon, who led the vaccine's clinical trials, says in a draft paper with colleagues that four days, "would be too slow if an individual was exposed to a lethal [meningococcal] load".
Attention has focused on the vaccine's brief protection - although considered by its backers enough to help end the epidemic - since the Herald on Monday summarised a report from the university's Immunisation Advisory Centre. It said "the detectable duration of immunity post-vaccination is measured in months rather that years".
Maternity services campaigner Lynda Williams is concerned that parents might inadvertently endanger their vaccinated children by not acting on possible meningococcal infection symptoms because the brevity of protection was not clearly spelled out.
Professor Lennon said that although it would have been better if more information had been given to parents on this, health authorities had not conspired to withhold it.
"I'm not sure it was wilful. It's more the excitement of the chase, trying to get it [the vaccine] out there, trying to get things organised, perhaps not looking at the situation five years down the track where the situation is much more complicated. People in public health campaigns tend to want simple messages; it's complex."
The short duration of protection conferred by the MeNZB vaccine was known from earlier scientific literature on a similar vaccine, although there were uncertainties, and from the New Zealand clinical trials which were completed before the vaccination campaign began.
The Ministry of Health says it did explain - in a leaflet for parents and young people - that protection was expected to last for a few years although the exact period was unknown. It says this was the best information then available and as new details became available they were shared with GPs and practice nurses.
