Australian vaccine preventable disease epidemiological review series: Pertussis, 2013-2018.

INTRODUCTION: Significant recent changes in Australian pertussis immunisation policy include the progressive introduction of funded pertussis immunisation programs for pregnant women, from late 2014 to mid-2015 at jurisdictional level and then under the National Immunisation Program from July 2018, and reintroduction of the 18-month booster dose in 2016. This study analyses pertussis notification, hospitalisation, and mortality data from 2013 to 2018 in the context of trends since 1995. METHODS: This study used data from the National Notifiable Diseases Surveillance System, the National Hospital Morbidity Database, and the Australian Coordinating Registry, for descriptive analysis of pertussis notifications, hospitalisations and deaths in Australia by Aboriginal and Torres Strait Islander (Indigenous) status from 2013 to 2018, examining trends between 1995 and 2012 at both the national and jurisdictional level. Incidence rate ratios (IRR) were utilised to compare pertussis incidence in infants aged < 2 months and 6-11 months for each year from the 2015-2018 (post-maternal-vaccination) period against the 2010-2013 (pre-maternal-vaccination) period. RESULTS AND DISCUSSION: Annual national all-age incidence of pertussis notifications between 2013 and 2018 was 63.6 per 100,000 population, 40% less than between 2006 and 2012. Between 2016 and 2018, infants aged < 2 months had the lowest notification rates of age groups < 5 years old, with the highest notification rates in pre-adolescents aged 9-11 years. Compared with the baseline period (2010-2013), the IRR for infants aged < 2 months decreased in each year during the post-maternal-vaccination period from 0.4 (95% confidence interval [95% CI]: 0.3-0.5) in 2015 to 0.1 (95% CI: 0.1-0.2) in 2018. For infants aged 6-11 months, the IRR was 0.9 (95% CI: 0.8-1.0) in 2015, 1.1 (95% CI: 1.0-1.2) in 2016 and declined to 0.7 (95% CI: 0.6-0.8) in 2017 and 2018. Notification and hospitalisation rates in Indigenous children were 3-8 times as high as rates in non-Indigenous children across all age groups < 5 years old. CONCLUSION: Pertussis remains the second most frequently notified vaccine preventable disease in Australia, after influenza, but dramatic decreases in incidence have been observed in infants too young to receive any doses of pertussis-containing vaccine.

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

INTRODUCTION: Invasive Haemophilus influenzae 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.

Rotavirus Epidemiology and Monovalent Rotavirus Vaccine Effectiveness in Australia: 2010-2017.

BACKGROUND: Rotavirus vaccine has been funded for infants under the Australian National Immunisation Program since 2007, with Rotarix vaccine used in New South Wales, Australia, from that time. In 2017, New South Wales experienced a large outbreak of rotavirus gastroenteritis. We examined epidemiology, genotypic profiles, and vaccine effectiveness (VE) among cases. METHODS: Laboratory-confirmed cases of rotavirus notified in New South Wales between January 1, 2010 and December 31, 2017 were analyzed. VE was estimated in children via a case-control analysis. Specimens from a sample of hospitalized case patients were genotyped and analyzed. RESULTS: In 2017, 2319 rotavirus cases were reported, representing a 3.1-fold increase on the 2016 notification rate. The highest rate was among children aged <2 years. For notified cases in 2017, 2-dose VE estimates were 88.4%, 83.7%, and 78.7% in those aged 6 to 11 months, 1 to 3 years, and 4 to 9 years, respectively. VE was significantly reduced from 89.5% within 1 year of vaccination to 77.0% at 5 to 10 years postvaccination. Equinelike G3P[8] (48%) and G8P[8] (23%) were identified as the most common genotypes in case patients aged ≥6 months. CONCLUSIONS: Rotarix is highly effective at preventing laboratory-confirmed rotavirus in Australia, especially in infants aged 6 to 11 months. Reduced VE in older age groups and over time suggests waning protection, possibly related to the absence of subclinical immune boosting from continuously circulating virus. G8 genotypes have not been common in Australia, and their emergence, along with equinelike G3P[8], may be related to vaccine-induced selective pressure; however, further strain-specific VE studies are needed.