Feature

Immunisation Debate

Health researchers are concerned that a third of New Zealand children are not fully immunised, and are worried about the potential for epidemics of measles, diptheria and other killer diseases.

By Vicki Hyde, NZSM

The New Zealand population, on the whole, is a fairly healthy one, but health researchers are concerned that apparently falling levels of immunisation in New Zealand children may see a return to epidemics of polio, measles and whooping cough.

Last year, a pilot survey of children in the Hawke's Bay region showed that only around 60% were getting the full set of immunisations recommended, and that this number dropped to around half in the Maori population.

In New Zealand, children are vaccinated against eight main infectious diseases: diptheria, tetanus, polio, hepatitis B, measles, mumps, rubella and pertussis (whooping cough). Vaccinations take place at six weeks of age, three months, five months, 15 months, and 18 months.

The survey showed that most children were getting the first three sets of vaccinations, but that there was a marked falling off of immunisations at the 15-month and 18-month stages. Dr Michael Baker, epidemiologist at the Communicable Diseases Centre, sees a number of reasons for this.

"The parents probably see less reason for immmunising [at that stage]. They're often out of contact with the health system by then, and the children are healthier so there's less opportunity of visits," he explains.

Active opposition to immunisation was rare, rather it was a case of just "not getting around to it". The study found that children of people in the lower socio-economic brackets were at the greatest risk of incomplete immunisation.

"The groups who miss out here miss out in other areas as well," Baker notes.

The survey is now being repeated at a national level, and has been expanded to gather more information on parental attitudes towards immunisation. Baker sees the expanded survey as providing a good baseline from which to examine immunisation practices in New Zealand. Data on immunisation rates has been sketchy, and the pilot survey found considerable discrepancies between GP records, the children's individual health record books, and parental recall.

Polio

Poliomyelitis was once a major problem in New Zealand and around the world. At its worst, it resulted in death, but its better known legacy is the paralysis it causes.

Two vaccines are used to control polio. The Sabin vaccine is a form of live, weakened poliovirus taken orally, while the Salk vaccine is a dead virus injection. Concerns about possible reaction to the Sabin vaccine led to a World Health Organisation study, which concluded that the risk of vaccine-associated polio was less than one in a million, with other studies placing it closer to one in three million. Four oral doses of the Sabin vaccine is standard in New Zealand.

Denis Hogan, of the Post-Polio Support Group, believes that some of the resistance towards polio vaccination stems from people no longer being familiar with the havoc which the disease itself once caused.

"We need to keep the benefits to the community in front of us," Hogan avers. He recalls polio epidemics when children were not able to travel, and when schools, theatres and swimming pools were closed down in times of almost national panic. The nearest modern equivalent has been the meningitis scares at the universities in Christchurch and Auckland.

"We certainly don't want that back again," he says.

One unlooked-for problem with the successful control of polio is that many of the doctors now treating members of the Post-Polio Group have had very little experiencing with the condition. The last reported case of polio in New Zealand was in 1961, although there have been four cases since 1964 associated with the vaccine itself. Ironically, one possible way of contracting polio these days is when unimmunised adults change the nappies of babies who have just been vaccinated.

Diptheria, Whooping Cough

Diptheria, tetanus and pertussis are commonly linked in immunisation circles, as the one vaccination is used to immunise against all three diseases. Of the common vaccines, this triple antigen is the one most likely to result in adverse reactions, but it is also considered one of the most vital because of the seriousness of the complaints involved.

Diptheria was one of the most dangerous of childhood diseases, with its bacteria smothering the respiratory tract and poisoning the heart, kidneys and liver. It doesn't respond well to antibiotics, but the development of a vaccine for it has helped wipe it out in developed nations.

Dr Stewart Reid, paediatrician and chairman of the Communicable Diseases Advisory Committee, admits that there have been no cases of diptheria in New Zealand for quite a long time, but maintains that it is still present. He is convinced that if immunisation levels were to drop sufficiently, diptheria epidemics would rage once more.

"We don't actually want to prove that," he hastens to add. "I certainly don't want to be a part of that."

Pertussis is better known as whooping cough, a complaint that can be deadly in babies, although much more mild in older children. It can cause convulsions, brain inflammation, permanent brain damage and death. Because of its severity in babies, vaccination against whooping cough is one of the earliest, being done at six weeks with the triple antigen, with two further booster shots.

In Australia, the death rates from whooping cough were just over 41 per 100,000 cases during 1927-1936. After the vaccine was developed and an immunisation programme became routine, this dropped to 0.13 in 1967-1976.

Occasional epidemics still occur, partly because the vaccine is not totally effective and partly because there have been recurring campaigns against this vaccination. The UK suffered a particularly severe outbreak as a result of immunisation levels dropping from 80% to almost 30% in the late 70s. Within two years there were almost 300 deaths per 100,000 reported cases.

The UK epidemic was mirrored by one here, which prompted a vaccination change from two doses to three doses against whooping cough. Although New Zealand immunisation rates hadn't fallen as in the UK, the outbreak here was still serious. Reid notes that New Zealand is still very conservative as regards pertussis immunisation -- in the US, five doses are given against the disease.

Measles, Rubella, Mumps

Most people see measles as a standard childhood disease that presents few problems beyond the characteristic rash. In developing countries it kills, and is responsible for almost a million deaths annually in Africa and other parts of the Third World.

"Measles is a dreadful killer," asserts Reid. "As with all these things, it affects the less well nourished so much more."

It has caused problems in recent years, with measles epidemics in various parts of New Zealand.

"We've had a major measles epidemic in which four children died," he says. Thousands of cases were reported with children off school and infected parents off work. Over a hundred cases of serious ear infections resulted.

"This is all essentially preventable by a good immunisation programme," he says. The epidemic is directly attributable to sufficient numbers of children not being adequately immunised, he adds.

One of the primary concerns about the measles vaccine is the chance of brain inflammation, or encephalitis. This is found to occur in one in a million doses, and there are still doubts about whether there is a link there. In contrast, those contracting "wild" measles run an encephalitis risk of one in a thousand cases, making it considerably more dangerous.

Rubella, also known as German measles, is a fairly mild disease in children. It becomes more significant in pregnant mothers, where contracting the disease can result in congenital defects in the baby, including blindness, deafness and mental retardation. Consequently, immunisation programmes have tended to concentrate on ensuring that pre-pubertal girls are vaccinated against the disease.

In New Zealand last year, three cases of congenital rubella were reported, where babies suffered brain damage and birth defects because their unimmunised mothers caught rubella during pregnancy.

Immunisation Concerns

Arguments against immunisation are made on a number of grounds, ranging from personal freedom to concerns about possible side effects of the immunisation process.

"Their concerns do have to be listened to," acknowledges Baker. "We do have an obligation to explain medical intervention to people."

Reid believes that parents who deliberately choose not to have their children immunised at least have the responsibility to tell those children later in life. He's familiar with cases where people have wanted to take up medical or nursing courses, or travel overseas, but haven't been sure of their immunisation history. Immunisation at a late age is more difficult than during childhood.

To counter some of these problems, Reid would like to see the establishment of a national immunisation register and recall system, something like the cervical smear register currently being set up. He recognises that it will take quite some time for support and funding for such a register to develop.

Some critics of immunisation suggest that, because the diseases are now controlled, vaccination against them is no longer required. This argument tends to exasperate health researchers, who counter that the diseases are under control at present precisely because of immunisation programmes.

"If there was no immunisation against measles, everyone would get it, likewise with polio," Reid observes. Such tends to be the case in those countries without organised programmes, such as the Philippines and Turkey.

"More needs to be done about children who are apparently adversely affected by immunisation," Reid agrees. He's concerned at the very few cases where there is an apparent connection between a vaccination and a severe reaction. In these cases, it can be very difficult to definitively prove a connection between the vaccine and, for example, brain damage. Reid has seen some terrible struggles on the parts of parents required to furnish proof of such a connection, and he would like to see a "no blame" provision for compensation in such cases.

Fortunately, such problems are extremely rare.

Despite some of the more alarmist claims, it is generally accepted that the cost-benefit analysis of immunisation shows that the benefits are very high and the costs very low. In a report on New Zealand recommendations in New Ethicals, Reid said:

"No vaccine is ever 100% safe or effective. The decision to recommend vaccination, like all interventions in medicine, is one of balance; the risks of the proposed action are less than the risks of no action, considerably less in the case of vaccines... Although no schedule can ever be perfect, the medical profession and the public of New Zealand can have considerable confidence in our childhood immunisation schedule."

Vicki Hyde is the editor of New Zealand Science Monthly.