It is all about timing. Long and dedicated practice is required to achieve good timing. All athletes and performing artists know this.

The timing of our immunisation schedule is similarly based upon lessons learnt from long and dedicated research and clinical practice. In order to protect those most vulnerable to severe disease it is necessary to start immunisation at as young an age as possible. However, the capacity for the immune system to respond to an immunising stimulus is reduced in young infants. A compromise is therefore required to protect the youngest but also maintain protection through childhood and beyond. In addition, for most vaccines the immune response to a single dose is sub-optimal compared to that achieved with two or more doses.

This compromise is achieved by dividing the primary immunising dose into three—with at least 4 weeks between each dose, followed by booster doses of most of the antigens after subsequent longer intervals. Thus, in New Zealand, the primary series of diphtheria, tetanus, pertussis, polio, hepatitis B*, and Haemophilus influenzae type b† vaccines is delivered at ages 6 weeks, 3 months, and 5 months—with subsequent boosters in childhood and adulthood.

How important is it to start immunisation at 6 weeks of age? Can a few weeks really make such a difference? On-time delivery of the first infant vaccine doses is a keystone to successful immunisation. This is not only because young infants remain at risk of severe and sometimes fatal disease, most notably from pertussis, but also because delay in receipt of the first vaccine dose is one of the strongest and most consistent predictors of subsequent incomplete immunisation.1,2

Research from New Zealand confirms the importance of timeliness. During the 1995 to 1997 pertussis epidemic, delay in receipt of any of the three infant doses of pertussis vaccine was associated with a four-fold increased risk of hospitalisation with pertussis.3 In the 1996 North Health regional immunisation survey, being delayed for the 6-week immunisation was associated with a 16-fold increased risk of incomplete immunisation at age 2 years.4

In this issue of the Journal, data is reported from the Pacific Islands Families Study on the proportion of infants whose mothers stated they had not received the 6-week immunisations, and the factors associated with non-receipt of these vaccines.5

This important longitudinal study has established a cohort of 1590 New Zealand-born infants of Pacific ethnic groups, 1376 (86%) of whom were visited at home at approximately 6 weeks of age. Immunisation is of particular relevance to this cohort. Pacific children experience an excessive burden from vaccine preventable disease—with hospital admission rates for measles being five times greater (and for pertussis almost two times greater) than for European children.6,7

Approximately 27% of mothers said their child had not yet received the 6 week immunisation. Data was collected for 105 (8%) of the children when they were less than 6 weeks old, 865 (63%) when 6 to 8 weeks old, and 406 (29%) when more than 8 weeks old. Thus some were too young to have yet received the vaccines. The data presented does not enable measurement of the proportion whose immunisations were delayed. Also, verification from written immunisation records is necessary to be confident of the proportion of infants receiving all of the vaccines scheduled at age 6 weeks.

With these qualifications what do we learn from this study? First, this manuscript reminds us that a sustainable reliable method for measuring immunisation coverage in New Zealand has yet to be established. As we have had an immunisation schedule in New Zealand for over 40 years now, this is long overdue. The most reliable coverage data we have is from the 1977 Christchurch Birth Cohort Study and from the national and regional immunisation surveys performed in 1991–92 and 1996.4,8,9 These studies showed that, since the 1970s, between 70% and 90% of children have received the primary infant vaccine series. The immunisation surveys from the 1990s showed that between 80% and 90% of children receive the primary series, with no more than 60% of children at age 2 years having received all scheduled immunisations.4,9 There has only been a very small increase in immunisation coverage over the past 25 years. It is difficult to improve something that is not measured.

In developed countries, the three major contributors to incomplete immunisation are socioeconomic factors, healthcare factors, and parental attitudes. Healthcare factors include healthcare system barriers, provider beliefs, variability in provider practices and missed opportunities to immunise. In New Zealand, in contrast with the repeated examination of family demographics as predictors of immunisation status, examination of the health system and health professional contributions to incomplete immunisation has been less intense. Indeed, relative to the literature from other developed countries, the lack of investigation of these factors in New Zealand is notable.

Secondly, the Pacific Islands Families Study identified factors associated with non-immunisation. In addition to age and ethnic group, and after adjustment for confounding variables, children of mothers who were Pacific born, who had difficulty with transport, or who had more than five children were less likely to be immunised.5

The first two of these factors imply that the relationship between the family and the primary care provider contributes to incomplete immunisation. Mothers born in the Pacific may be more familiar with community-based methods of vaccine delivery (as used in several Pacific Island nations) and less aware of the need in New Zealand to find a primary care provider for their infant plus one for their own pregnancy-related health needs.

Difficulties with transport indicate an access barrier to primary care for those too poor to have a reliable vehicle. Poverty hinders immunisation not only because of its negative impact upon how the household functions but also because those who are poor do not have the same access to high-quality primary care as those who are not poor.

Given the importance of household transmission in spreading diseases such as pertussis to vulnerable infants, to be the youngest of six children, and yet be incompletely immunised, is a public health failure.10

The requirements for improved immunisation coverage and timeliness have been well defined. Countries with higher immunisation rates than New Zealand have achieved this by using multifaceted immunisation strategies. Recent examples included Australia’s Seven Point Plan and the United States’ Childhood Immunization Initiative.11,12 Australia’s plan included monetary incentives for parents, incentives for general practitioners, a range of educational incentives, school entry legislation, enhanced research activity, and development of a national immunisation register.11

A similar blueprint has already been developed for New Zealand. It was stated comprehensively by the National Health Committee in 1999.13 The key elements are national leadership and coordination of immunisation, development of a complete national immunisation information system, ensuring a stronger relationship between each child and an identified primary care provider, and greater accountability of each primary care provider for immunising all children.

Australia’s Seven Point Plan and the United States’ Childhood Immunization Initiative were introduced in response to national perceptions that the burden from immunisation preventable disease was unacceptably high. The burden from immunisation preventable disease has remained unacceptably high in New Zealand for decades—so what are we waiting for?

Author information: Cameron C. Grant, Associate Professor, Paediatrics, University of Auckland (and Paediatrician, Starship Children’s Hospital), Auckland

Correspondence: Dr Cameron Grant, Department of Paediatrics, Faculty of Medicine and Health Sciences, University of Auckland, Private Bag 92019, Auckland. Fax: (09) 373 7486; email: cc.grant@auckland.ac.nz