Immunization coverage against invasive pneumococcal disease among children in the capital health region of Alberta

Volume 31-06  15 March 2005

Introduction

Invasive pneumococcal disease (IPD) is caused by the bacterium Streptococcus pneumoniae(1). IPD is a major cause of morbidity and mortality in young children < 5 years of age(2). The invasion of S. pneumoniae into the lungs (pneumonia), bloodstream (bacteremia), and fluid or tissues of brain and spinal cord (meningitis) can lead to death. IPD is a significant public health problem in child populations with this infection.

S. pneumoniae has 90 serotypes. Seven common pneumococcal serotypes (4, 6B, 9V, 14, 18C, 19F, and 23F) that cause approximately 80% of IPD in young children were isolated from the blood or cerebrospinal fluid of children < 6 years in the United States(3,4). The 7-valent pneumococcal conjugate (PCV7) vaccine includes those seven pneumococcal serotypes. Vaccination with the PCV7 (Prevnar®, Wyeth-Ayerst, Canada)(5) has been integrated into the standard immunization program for children in Alberta since July 2002, in accordance with the National Advisory Committee on Immunization recommendation(6) (at the age of 2, 4, and 6 months followed by a booster at 12 to 15 months).

The purpose of this paper is to estimate the degree of immunization coverage by the PCV7 vaccine program among all children in the Capital Health Region of Alberta, including those in the three contiguous First Nations reserves, and separately identifying children in (low-income) families that receive premium assistance and children in First Nations families, on and off reserve.

Methods

Before initiation of the project, ethics approval was obtained from the Health Research Ethics Board of the University of Alberta and the Research Ethics Board, Health Canada.

The study population consisted of all children, newborns, and new residents with dates of birth between 1 July and 31 December, 2002, in the Capital Health Authority (CHA). Immunization data on the study population came from two sources. The CHA collects data on all children who are eligible for immunization and on all vaccination visits within the region in its Case Works program. The Alberta Region of the First Nations and Inuit Health Branch (FNIHB), Health Canada, provides information on First Nations children living on reserve in the three contiguous reserves. The CHA and FNIHB collected 12 months’ immunization data between 1 July, 2002, and 30 June, 2003, on all study children for PCV7 vaccine and Pentacel® (Aventis Pasteur, Toronto, Ontario), the DTaP/Hib/IPV vaccine against diphtheria, tetanus, acellular pertussis, Haemophilus influenzae type b, and inactivated polio, which was used for comparison.

Two original immunization data sets were provided to Alberta Health and Wellness. The Health Surveillance Branch staff combined the two data sets and performed the record cleaning process. Missing information such as demographic or personal health number (PHN) was added, using the search results from the Alberta Central Stakeholder Registry database. Immunization records with the completed PHN were merged with the Alberta Stakeholder Registry-based mid-year population to obtain socio-economic information. Health Surveillance Branch staff then scrambled the PHNs to create an anonymous identification for each individual before sending the new immunization data file for analysis to the Institute of Health Economics.

To evaluate the immunization coverage of the program we focused on how many children started and completed their vaccine regimens (excluding boosters) (n = 4,733).The completion criterion for DTaP/Hib/IPV was whether an infant had received three vaccinations by the end of 12 months of age. The completion criteria for PCV7 were defined on the basis of the age at the first PCV7 vaccination. For children who received their first PCV7 vaccine at 7 months there should be three PCV7 vaccinations received before the age of 12 months with an interval of not < 4 weeks between any 2 doses. Further, it is necessary that the first vaccination should not be earlier than 6 weeks after birth. For children who received their first PCV7 vaccine at 7 months of age there should be two PCV7 vaccinations received, and the interval between doses should not be < 4 weeks.

We compared the immunization completion rates between First Nations children and non-First Nations children. In the non-First Nations group we compared children of low-income families (families that received assistance with their health premiums) with other children.

Results

Almost all children started the PCV7 program, the lowest rate being among First Nations children on reserve (94% versus 98% for non-First Nations children). The overall immunization coverage rate for three doses of vaccine was 93.7% for DTaP/Hib/IPV and 91.9% for PCV7 (excluding boosters). The coverage rate among children of families that received full assistance for health premiums (low-income families) was 91.5% for DTaP/Hib/IPV and 90.5% for PCV7 (n = 749). Among those who did not receive premium assistance the coverage was 95.3% for DTaP/Hib/IPV and 93.4% for the PCV7 (n = 3,783, < 0.01). While the initiation rates of the DTaP/Hib/IPV and PCV7 were comparable, the completion rates were significantly lower among First Nations on and off reserve.

Discussion

We conducted an analysis of the degree of 1-year coverage for pneumococcal immunization during the first 6 months’ intake of a provincial program on universal vaccine coverage, within the Capital Health (Edmonton) Region. Both uptake and completion rates were lower for PCV7 than for DTaP/Hib/IPV and, despite high initiation, full coverage was lower among First Nations and lower-income individuals than for the remainder of the population.

There are several limitations of the analysis. The follow-up period was not long enough to capture booster doses for PCV7 and the primary series PCV7 vaccinations for those who started late. Boosters seem to have an important role in the immunogenic effects of vaccines and in an ideal situation should be considered for evaluation of a comprehensive immunization program(7).

The unavailability of follow-up data beyond 12 months may have resulted in an underestimate of the completion rate for those children who received their vaccinations on a late schedule; however, it may also have resulted in an overestimate of the completion rate for those who received their primary series but failed to receive their booster doses.

In conclusion, the rate of administration of at least one dose of PCV7 vaccine was high for all children. The completion of the PCV7 vaccination program was also relatively high in the non-First Nations population. The uptake and completion rates of the PCV7 and DTaP/Hib/IPV vaccines resembled each other in all population groups of the study, indicating that the PCV7 vaccine program has been accepted by parents as potentially beneficial immunization for their children.

Table 1. Uptake and completion rates of PCV7 and DTaP/Hib/IPV vaccines in different subgroups of children in the Capital Health Region, Alberta

 

n

PCV7

DTaP/Hib/IPV

Uptake %

Completion %

Uptake %

Completion %

All First Nations

201

98.0

68.7

98.5

72.1

On reserve

50

94.0

44.0

94.0

58.0

Off reserve

151

99.3

76.8

100.0

76.8

Non-First Nations

4,532

98.1

92.9

99.7

94.6

Health premium receivers
(low-income families)

749

98.8

90.5

100.0

91.5

Non-health premium receivers

3,783

98.0

93.4

99.7

95.3

All populations

4,733

98.1

91.9

99.7

93.7


Acknowledgements

This paper is based on a project that was supported by the Institute of Health Economics in Edmonton. We would like to thank the First Nations' community staff and health directors for their contribution and facilitation of this work.

References

  1. O’Brien KL, Shaw J, Weatherholtz R et al. Epidemiology of intensive Streptococcus pneumoniae among Navajo children in the era before use of conjugate pneumococcal vaccines, 1989-1996. Am J Epidemiol 2004;160(3):270-78.

  2. O’Brien KL, Santosham M. Potential impact of conjugate pneumococcal vaccines on pediatric pneumococcal disease. Am J Epidemiol 2004;159(7):534-644.

  3. WHO. INT. Immunization, vaccines and biologicals. Pneumococcal vaccines. URL: ttp://www.who.int/vaccines/en/pneumococcus.shtml.

  4. Centers for Disease Control and Prevention. Preventing pneumococcal disease among infants and young children. Recommendations of the Advisory Committeee on Immunization Practices (ACIP). MMWR 2000;49(RR-9).

  5. Canadian Pediatric Society. Pneumococcal vaccine for children. Pediatr Child Health 2002;6(4):214-17.

  6. National Advisory Committee on Immunization. Canadian immunization guide, 6th ed. Ottawa: Health Canada, 2002.

  7. Rennels MB, Edwards KM, Keyserling HL et al. Safety and immunogenicity of heptavalent pneumococcal vaccine conjugated to CRM197 in United States infants. Pediatrics 1998 101(4 Pt 1):604-11.

Source: K Golmohammadi, MD, Research Associate, Institute of Health Economics, Edmonton; T-H Nguyen, BSc, Health Data Analyst, Alberta Health and Wellness; A Hanrahan, MN, Director, Communicable Disease Control, CHA; P Jacobs, DPhil. Professor, Public Health Sciences, University of Alberta; G Predy, MD, Medical Officer of Health, CHA; D Rose, MBA, Regional Manager, Planning and Support, Community Health Services, CHA; J Loewen, Assistant Director, Communicable Disease Control, CHA; R Richardson, RN, Nurse Manager, Communicable Disease Control, FNIHB - Alberta Region; W Yacoub, MB, ChB, FRCPC, Medical Officer of Health, FNIHB - Alberta Region; A Ohinmaa, PhD, Associate Professor, Public Health Sciences, University of Alberta.


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