To provide adequate direct and indirect protection against vaccine-preventable diseases (VPD), a high proportion of the population needs to be immune. Specific immunity against certain diseases can be achieved through immunisation with vaccines or exposure to the pathogen itself. The aim of immunisation programmes is to generate immunity in individuals and within the community to prevent the spread of disease and to reduce the impact of such diseases.
Infants and young children are at highest risk of infectious disease due to a lack of prior experience and immunity, and immature immune responses. For this reason, national immunisation programmes begin in early infancy (at 6 weeks of age in New Zealand). The timeliness as well as the uptake of vaccines is an important factor in providing protection to young children. Delays in vaccine dose timing can leave infants unprotected and vulnerable to severe disease. Optimally, immunisation coverage needs to be over 95% to provide the best protection against VPDs, especially the most contagious diseases such as pertussis and measles.
The Ministry of Health has monitored immunisation coverage and timeliness since the 1990s. For more than two decades, there has been concerted and successful efforts to improve immunisation coverage in New Zealand (NZ) and elsewhere to reduce gaps in equity and encourage uptake of vaccines by all. However, in NZ, despite excellent progress, coverage has failed to consistently reach the 95% community immunity threshold, and barriers and equity gaps remain. Recently, gaps in coverage have been widening, particularly at the 6-months mark, as measurement of timeliness of delivery and equity gaps have widened, particularly for children of Māori ethnicity and for those living with high socioeconomic deprivation.
This evidence-based review of recently published literature was conducted to identify and examine core drivers that potentially affect vaccine uptake and immunisation coverage of the National Immunisation Schedule childhood vaccines. The literature reviewed was published primarily between January 2012 and July 2018.