Elsevier

Vaccine

Volume 39, Issue 12, 19 March 2021, Pages 1727-1735
Vaccine

Estimating pneumococcal vaccine coverage among Australian Indigenous children and children with medically at-risk conditions using record linkage

https://doi.org/10.1016/j.vaccine.2021.02.015Get rights and content

Abstract

Background

Risk-based recommendations are common for pneumococcal vaccines but little is known about their uptake. In Australia, pneumococcal conjugate vaccine (PCV) was funded only for Aboriginal or Torres Strait Islander (Indigenous) children and those with underlying medical conditions in 2001, and then there were different booster dose recommendations depending on risk after the introduction of universal PCV vaccination in 2005.

Methods

We measured coverage of PCV dose 3 and additional PCV and 23-valent pneumococcal polysaccharide vaccine (PPV23) doses by risk group among children born in July 2001–December 2012 in two Australian states using linked immunisation and hospitalisation data (available until December 2013). We ascertained medical risk conditions using hospitalisation diagnosis codes and Indigenous status using an established algorithm, comparing coverage for children born pre (2001–2004) and post (2005–2012) universal PCV funding.

Results

Among 1.3 million children, 63,897 (4.9%) were Indigenous and 32,934 (2.5%) had at least one medically at-risk condition identified by age 6 months. For births in 2001–2004, coverage for PCV dose 3 by 1 year of age was 37% for Indigenous, 15% for medically at-risk and 11% in other children, increasing to 83%, 91% and 92%, respectively for births in 2005–2012. In children with medically at-risk conditions, PCV dose 4 coverage by 2 years was 1% for 2001–2004 births, increasing to 9% for 2005–2012 births, with PPV23 coverage by 6 years 3% in both cohorts. Among eligible Indigenous children, PPV23 coverage by 3 years was 45% for 2001–2004 births and 51% for 2005–2012 births.

Conclusions

Coverage with additional recommended booster doses was very low among children with medical conditions, and only modest among Indigenous children. If additional PCV doses are recommended for some risk groups, especially in the context of routine schedules with reduced doses (e.g. 2 + 1 and 1 + 1), measures to improve implementation will be required.

Introduction

Invasive pneumococcal disease (IPD) is infection with Streptococcus pneumoniae in a normally sterile site, most commonly bacteremia, meningitis or pneumonia. IPD incidence is highest in young children, the elderly, Aboriginal and Torres Strait Islander people (hereafter respectfully referred to as Indigenous) and in individuals with certain chronic medical conditions. Between 2011 and 2015, IPD notification rates among Indigenous people in Australia were 6.5 times higher for all ages and 3.4 times higher in children < 5 years of age than in the non-Indigenous population [1]. A recent study in New South Wales (NSW), Australia, found children ≤ 12 years of age who had at least one medical condition that put them at a higher risk (medically at-risk group) had a four-fold higher IPD incidence, with relative risks varying from 1.1 for those with heart disease to 26.4 for those with dysfunction of the spleen compared with children without medical risk conditions [2]. Similar estimates for those with medical risk conditions have been reported for other comparable countries [3], [4], [5].

In 2001, Australia initially funded the 7-valent pneumococcal conjugate vaccine (PCV7) under the National Immunisation Program (NIP) for all children with a medically at-risk condition and Indigenous children [6]. Indigenous children received a 3-dose primary course of PCV7 at 2, 4 and 6 months of age (3 + 0 schedule), while medically at-risk children received an additional dose of PCV7 at 12 months (3 + 1 schedule) and PPV23 at 4 to 5 years of age. Indigenous children living in four jurisdictions (Northern Territory (NT), Queensland (QLD), South Australia (SA) and Western Australia (WA) received a dose of PPV23 at 18 to 24 months of age following a 3 + 0 schedule of PCV7 [7]. In 2005, NIP funding for a 3 + 0 schedule of PCV7 was extended to all Australian children [7]. In 2011, PCV7 was replaced by PCV13 and in 2018, the schedule changed from 3 + 0 to 2 + 1 at 2, 4 and 12 months of age, but a 3 + 1 schedule continued for Indigenous children in high incidence regions and for medically at-risk children [8].

Estimating vaccine coverage for the targeted high-risk program has been difficult, although since the universal program was introduced in 2005, coverage by Indigenous status for the primary PCV course has regularly been reported using data on the Australian Childhood Immunisation Register (ACIR) [9], [10]. In the post-universal period, coverage for 3 doses of PCV at 12 months of age has been > 90% for non-Indigenous and > 85% for Indigenous children [9], [10], [11], [12], [13], [14], [15]. However, in the pre-universal era, coverage estimates for Indigenous children were inaccurate due to incomplete recording of Indigenous status on the ACIR [16]. Children with medically at-risk conditions were not identifiable in the ACIR and other Australian studies estimating their PCV and PPV23 coverage have been limited by small sample size, a focus on hospital settings or a single medically at-risk condition [17], [18], [19].

Linkage of ACIR and other administrative health data provides an opportunity to identify the medically at-risk children and to improve completeness of reporting of Indigenous status, particularly in the pre-universal era. The aims of this study were to estimate population coverage for PCV and PPV23 using linked ACIR and health data, in Indigenous children with and without medically at-risk conditions, and non-Indigenous children with medically at-risk conditions who were born in the pre- (2001–2004) and post-universal (2005–2012) periods.

Section snippets

Study population

We analysed data from a retrospective population-based cohort of 1.3 million children born between July 2001 and December 2012 in two Australian states - NSW and WA - which together represent 42% of the Australian total population and account for 125,000 births annually. Details of this cohort, datasets and linkage procedures are described elsewhere [20], [21], [22]. In brief, all the singleton live births who had a record in both state-based perinatal and birth registration datasets were

Results

We excluded 340 (0.02%) children from the cohort due to either incorrect dose order (n = 336) or a hospital admission for a medically at-risk condition before the date of birth (n = 4), leaving a base cohort of 1,313,560 children (Fig. 1). We found 336 (0.3%) duplicate records of PCV dose 4 and 38 (0.3%) children with two PPV23 doses. In the base cohort, 63,897 (4.9%) children were Indigenous: 43,805 from NSW and 20,092 from WA. There were 32,934 (2.5%) children with a medically at-risk

Discussion

To our knowledge this is the first population-based study to report coverage with the pneumococcal vaccine among medically at-risk children. We found that dose 3 PCV coverage, on-time or any-time, was very low before the introduction of a universal childhood vaccine program, at ≤ 15% for medically at-risk and < 40% for Indigenous children, despite being available free of charge to these populations. Following the introduction of the universal program, any-time coverage of PCV dose 3 for the

Conclusion

In our population-based study, coverage with recommended and funded booster doses for the medically at-risk and Indigenous children was unacceptably low. Improving awareness of targeted vaccination programs among service providers is important, especially given recent schedule changes in Australia (implementation of a 2 + 1 schedule at 2, 4 and 12 months of age for non-risk groups) [8] and consideration by some countries of routine schedules with reduced doses (e.g. 1 + 1 in the United Kingdom

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

Authors acknowledge the staff at the Population Health Research Network (PHRN) and participating PHRN data linkage and infrastructure nodes (the Western Australian Data Linkage Branch, the NSW center for Health Record Linkage, and the Australian Institute for Health and Welfare), and the WA and Commonwealth Departments of Health and NSW Ministry of Health who provided advice and data. The Aboriginal and Torres Strait Islander community and members of the Aboriginal Immunisation Research Group

Author contributions

AK, ATN, DR and HG conceptualised and designed the study, and reviewed and revised the manuscript. AK conducted the analysis and drafted the initial manuscript. RM, SS, SJ, PF, BL, HM, and PM provided expert advice on the study design, critically reviewed the study results, analysis methods and the manuscript. All authors approved the final manuscript as submitted and agreed to be accountable for all aspects of the work.

Sources of funding

This project was funded by the Population Health Research Network (PHRN), a capability of the Commonwealth Government National Collaborative Research Infrastructure Strategy and Education Investment Fund Super Science Initiative, and a National Health and Medical Research Council (NHMRC) project grant (APP1082342). A. Kabir is supported by a University International Postgraduate Scholarship (UIPA) from UNSW. H. Gidding, B. Liu and H. Moore are supported by NHMRC Fellowships.

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