Australian vaccine preventable disease epidemiological review series: invasive Haemophilus influenzae type b disease, 2000-2017.

INTRODUCTION

Invasive type b (Hib) disease is rare in Australia following vaccine introduction in 1993. Two deaths in vaccinated children in 2017, and the Hib booster dose moving from age 12 months to 18 months in 2018, prompted this review.

METHODS

Hib Case Surveillance Scheme 2000-2017 data were used to calculate incidence, incidence rate ratios (IRR) and vaccine failure (VF) trends. We used denominators from the Australian Immunisation Register to calculate incidence in immunised and unimmunised children.

RESULTS

All-age national invasive Hib disease incidence halved from 0.13 per 100,000 population in 2000 to 0.06 in 2017. Of 345 cases notified in 2000-2017, 153 were born post-2000, with 51 (33%) Aboriginal and Torres Strait Islander (Indigenous), and compared with non-Indigenous children IRR was 8.34 (95% CI: 5.83-11.79), with no evidence of decrease. Overall case fatality rate was 12.4% (19/153); 6 cases had underlying medical conditions. The overall incidence of invasive Hib disease was over 8 times higher (16.6 per 100,000) in children with no recorded doses than in children with ≥1 vaccine dose (1.9 per 100,000). VF criteria were met in 65/145 (45%) cases aged >8 weeks, of whom 7 (11%) were immunocompromised and 6 (9%) died, with no evidence of VF increase over time.

CONCLUSION

Overall, invasive Hib disease incidence declined by 55% from 2000 to 2017, but marked disparity persists between Indigenous and non-Indigenous children. Following moving the fourth dose from 12 to 18 months in 2018, monitoring of 3-dose VFs will be important, especially in Indigenous children.