Bulletin of the World Health Organization

The impact of adolescent pertussis immunization, 2004–2009: lessons from Australia

Helen E Quinn & Peter B McIntyre

Volume 89, Number 9, September 2011, 666-674

Table 4. Incidence rate ratios (IRRs)a for pertussis notifications in adolescents aged 12 to 19 years categorized as immunized or unimmunized by birth cohort, by epidemic periodb and jurisdictional group, Australia, 2004–2009

Jurisdictional groupingc Pre-programme epidemic rated (95% CI) IRR (95% CI)
2005–2007e
2008–2009f
Immunizedd Unimmunized Immunizedd Unimmunized
Australian Capital Territory/ South Australia/Victoria 92.6 (87.4–98.0) 0.23 (0.19–0.27) 0.33 (0.29–0.37) 0.54 (0.48–0.60) 1.00 (0.90–1.11)
New South Wales 156.8 (150.4–163.4) 0.17 (0.15–0.19) 0.26 (0.23–0.29) 0.87 (0.81–0.93) 1.85 (1.73–1.97)
Western Australia 284.2 (263.2–306.9) 0.02 (0.02–0.04) 0.06 (0.05–0.08) 0.04 (0.03–0.06) 0.04 (0.02–0.07)
Queensland 134.7 (127.1–142.8) 0.25 (0.15–0.39) 0.18 (0.14–0.22) 0.59 (0.51–0.67) 0.64 (0.58–0.71)
National 127.7 (123.0–132.6) 0.17 (0.16–0.19) 0.24 (0.22–0.26) 0.62 (0.59–0.66) 1.11 (1.06–1.17)

CI, confidence interval.

a These represent the ratios given by dividing the notification rate during each of the two epidemic periods after diphtheria, tetanus and acellular pertussis vaccine programme roll-out by the notification rate during the most recent epidemic period before programme roll-out.

b The recent epidemic periods used in the analysis were as follows: Australian Capital Territory, 2003; South Australia, 2001; Victoria, 2001/2002; New South Wales, 2000/2001; Queensland, 2001/2002; Western Australia, 2004; national, 2001.6

c Jurisdictional groupings were based on programme delivery characteristics.

d Per 100 000 population.

e For the period 2005–2007, data were limited to 2007 for Queensland.

f The single largest age group comprising each school grade was used to generate an approximate incidence among age groups, defined as immunized and unimmunized, with each grade defined as immunized if Tdap coverage was 50% or above.