Aditi Dey

Changes in hospitalisations for acute gastroenteritis in Australia after the national rotavirus vaccination program.

Objective: To evaluate the impact of the Australian rotavirus vaccination program on both rotavirus and all‐cause acute gastroenteritis (AGE) hospitalisations and to compare outcomes in Indigenous and non‐Indigenous people.

Fall in Genital Warts Diagnoses in the General and Indigenous Australian Population Following Implementation of a National Human Papillomavirus Vaccination Program: Analysis of Routinely Collected National Hospital Data

BACKGROUND Human papillomavirus (HPV) vaccination targeting females aged 12-13 years commenced in Australia in 2007, with catch-up vaccination of females aged 13-26 years continuing to 2009. Whole-population analyses, including effects on the Indigenous population, have not previously been reported. METHODS All hospital admissions between 1999-2011 involving a diagnosis of genital warts were obtained from a comprehensive national database. We compared the age-specific rates before to those after implementation of the vaccination program, according to sex and other characteristics. RESULTS Admission rates decreased from mid-2007 in females aged 12-17 years (annual decline, 44.1% [95% confidence interval {CI}, 35.4%-51.6%]) and from mid-2008 in females and males aged 18-26 years (annual declines, 31.8% [95% CI, 28.4%-35.2%] and 14.0% [95% CI, 5.1%-22.1%], respectively). The overall reductions from 2006-2007 to 2010-2011 were 89.9% (95% CI, 84.4%-93.4%) for females aged 12-17 years, 72.7% (95% CI, 67.0%-77.5%) for females aged 18-26 years, and 38.3% (95% CI, 27.7%-47.2%) for males aged 18-26 years. Compared with the average annual number before program implementation, about 1000 fewer hospital admissions involved a warts diagnosis during 2010-2011. Reductions after program implementation were similar for Indigenous (86.7% [95% CI, 76.0-92.7]) and non-Indigenous (76.1% [95% CI, 71.6%-79.9%]) females aged 15-24 years (P(heterogeneity) = .08). CONCLUSIONS National population-based hospital data confirm previous clinic-based reports of a marked decline in genital warts diagnoses among young people in Australia after program implementation, including indirect benefits to males. The impact of HPV vaccination appears to be similar in young Indigenous and non-Indigenous females.

Trends and patterns in vaccination objection, Australia, 2002-2013.

Objectives: To examine geographic and demographic trends in objection to vaccination in Australia.

Mapping information exposure on social media to explain differences in HPV vaccine coverage in the United States

BACKGROUND Together with access, acceptance of vaccines affects human papillomavirus (HPV) vaccine coverage, yet little is known about medias role. Our aim was to determine whether measures of information exposure derived from Twitter could be used to explain differences in coverage in the United States. METHODS We conducted an analysis of exposure to information about HPV vaccines on Twitter, derived from 273.8 million exposures to 258,418 tweets posted between 1 October 2013 and 30 October 2015. Tweets were classified by topic using machine learning methods. Proportional exposure to each topic was used to construct multivariable models for predicting state-level HPV vaccine coverage, and compared to multivariable models constructed using socioeconomic factors: poverty, education, and insurance. Outcome measures included correlations between coverage and the individual topics and socioeconomic factors; and differences in the predictive performance of the multivariable models. RESULTS Topics corresponding to media controversies were most closely correlated with coverage (both positively and negatively); education and insurance were highest among socioeconomic indicators. Measures of information exposure explained 68% of the variance in one dose 2015 HPV vaccine coverage in females (males: 63%). In comparison, models based on socioeconomic factors explained 42% of the variance in females (males: 40%). CONCLUSIONS Measures of information exposure derived from Twitter explained differences in coverage that were not explained by socioeconomic factors. Vaccine coverage was lower in states where safety concerns, misinformation, and conspiracies made up higher proportions of exposures, suggesting that negative representations of vaccines in the media may reflect or influence vaccine acceptance.

Evaluation of Australia's varicella vaccination program for children and adolescents.

OBJECTIVE This paper examines how the monovalent varicella vaccine for children, with an adolescent catch-up dose, was introduced into Australias National Immunisation Program (NIP), focusing on programme implementation. METHODS Semi-structured interviews were conducted with key informants involved in programme implementation. Key themes from interviews were identified through content analysis. Childhood coverage was assessed using data from the Australian Childhood Immunisation Register (ACIR) with adolescent coverage obtained from state/territory immunisation programmes. Seroprevalence data were analysed from national serosurveys conducted before and after programme commencement. RESULTS Implementation challenges for both parents and providers included: (a) parental report of previous infection as an exclusion criterion; (b) introducing a vaccine on its own at 18 months of age; and (c) adding the adolescent dose into existing school-based vaccination programmes with parental reported exclusion criteria. Despite these challenges, coverage rapidly reached 83% by 24 months of age and 30-33% for the adolescent catch-up dose. When considered in conjunction with estimated pre-vaccination natural immunity in both target groups (20% and 83%, respectively) coverage can be considered high. The serosurvey under-estimated coverage in 2-year-old children but was useful to assess trends in population immunity. CONCLUSION The introduction of a single dose of monovalent varicella vaccine at 18 months of age and a school-based catch-up programme at 11-13 years of age successfully achieved high coverage, notwithstanding some challenges. Reported natural infection has been an exclusion criterion for vaccination, but as the programme matures and circulation of wild-type virus decreases, the need for this warrants consideration. There is a need for sensitive laboratory assays to measure vaccine-induced immunity at a population level.

Estimating the measles effective reproduction number in Australia from routine notification data

OBJECTIVE To estimate the measles effective reproduction number (R) in Australia by modelling routinely collected notification data. METHODS R was estimated for 2009-2011 by means of three methods, using data from Australias National Notifiable Disease Surveillance System. Method 1 estimated R as 1 - P, where P equals the proportion of cases that were imported, as determined from data on place of acquisition. The other methods estimated R by fitting a subcritical branching process that modelled the spread of an infection with a given R to the observed distributions of outbreak sizes (method 2) and generations of spread (method 3). Stata version 12 was used for method 2 and Matlab version R2012 was used for method 3. For all methods, calculation of 95% confidence intervals (CIs) was performed using a normal approximation based on estimated standard errors. FINDINGS During 2009-2011, 367 notifiable measles cases occurred in Australia (mean annual rate: 5.5 cases per million population). Data were 100% complete for importation status but 77% complete for outbreak reference number. R was estimated as < 1 for all years and data types, with values of 0.65 (95% CI: 0.60-0.70) obtained by method 1, 0.64 (95% CI: 0.56-0.72) by method 2 and 0.47 (95% CI: 0.38-0.57) by method 3. CONCLUSION The fact that consistent estimates of R were obtained from all three methods enhances confidence in the validity of these methods for determining R.

Verification of measles elimination in Australia: Application of World Health Organization regional guidelines.

Background: The World Health Organization (WHO) Western Pacific Region (WPR) Guidelines on verification of measles elimination were established in 2012. This article outlines Australia’s approach to addressing the guideline’s five lines of evidence, which led to formal verification of elimination by the WHO Regional Verification Commission (RVC) in March 2014. Methods: The criteria were addressed using national measles notifications, data from selected laboratories, the national childhood immunization register, and three national serosurveys (1998/1999, 2002, 2007). Results: Australia met or exceeded all indicator targets with either national or sentinel data. Laboratory and epidemiological surveillance were of high quality, with 85% of cases documented as imported/import-related (target 80%); coverage with the first dose of measles vaccine was close to 94% in 2008–2012 and second dose coverage increased to 91% in 2012 (target >95%). There is ongoing commitment by the Australian Government to increase immunization coverage, and the absence of sustained transmission of any single measles genotype was demonstrated. Conclusions: This is the first documentation of the successful application of the WPR RVC guidelines. The indicators afford some flexibility but appear to provide appropriate rigor to judge achievement of measles elimination. Our experience could assist other countries seeking to verify their elimination status.

Evaluation of Combination Measles-Mumps-Rubella-Varicella Vaccine Introduction in Australia

Importance Incorporating combination vaccines, such as the measles-mumps-rubella-varicella (MMRV) vaccine, into immunization schedules should be evaluated from a benefit-risk perspective. Use of MMRV vaccine poses challenges due to a recognized increased risk of febrile seizures (FSs) when used as the first dose in the second year of life. Conversely, completion by age 2 years of measles, mumps, rubella, and varicella immunization may offer improved disease control. Objective To evaluate the effect on safety and coverage of earlier (age 18 months) scheduling of MMRV vaccine as the second dose of measles-containing vaccine (MCV) in Australia. Design, Setting, and Participants Prospective active sentinel safety surveillance comparing the relative incidence (RI) of FSs in toddlers given MMRV and measles-mumps-rubella (MMR) and a national cohort study of vaccine coverage rates and timeliness before and after MMRV vaccine introduction were conducted. All Australian children aged 11 to 72 months were included in the coverage analysis, and 1471 Australian children aged 11 to 59 months were included in the FS analysis, with a focus on those aged 11 to 23 months. Main Outcomes and Measures MMRV vaccine safety, specifically, the RI of FSs after MMRV vaccine at age 18 months, compared with risk following MMR vaccine and vaccine uptake for 2-dose MCV and single-dose varicella vaccine, focusing on timeliness. Results Of the 1471 children, the median age at first FS was 21 months (interquartile range [IQR], 14-31 months). Three hundred ninety-one children were aged 11 to 23 months and had at least 1 FS included in the analysis; of these, 207 (52.9%) were male. A total of 278 children (71.1%) had received MMR followed by MMRV vaccine, 97 (24.8%) had received MMR vaccine only, and 16 (4.1%) had received neither vaccine. There was no increased risk of FSs (RI, 1.08; 95% CI, 0.55-2.13) in the 5 to 12 days following MMRV vaccine given as the second MCV to toddlers. Febrile seizures occurred after dose 1 of MMR vaccine at a known low increased risk (RI, 2.71; 95% CI, 1.71- 4.29). Following program implementation, 2-dose MCV coverage at age 36 months exceeded that obtained at age 60 months in historical cohorts recommended to receive MMR vaccine before school entry, and on-time vaccination increased by 13.5% (from 58.9% to 72.4%). Despite no change in the scheduled age of varicella vaccine, use of MMRV vaccine was associated with a 4.0% increase in 1-dose varicella vaccine coverage. Conclusions and Relevance To our knowledge, this is the first study to provide evidence of the absence of an association between use of MMRV vaccine as the second dose of MCV in toddlers and an increased risk of FSs. Incorporation of MMRV vaccine has facilitated improvements in vaccine coverage that will potentially improve disease control.

Impact of the national targeted Hepatitis A immunisation program in Australia: 2000–2014

In November 2005, hepatitis A vaccine was funded under the Australian National Immunisation Program for Aboriginal and Torres Strait Islander (Indigenous) children aged 12-24months in the targeted jurisdictions of Queensland, South Australia, Western Australia and the Northern Territory. We reviewed the epidemiology of hepatitis A from 2000 to 2014 using data from the Australian National Notifiable Diseases Surveillance System, the National Hospital Morbidity Database, and Australian Bureau of Statistics causes-of-death data. The impact of the national hepatitis A immunisation program was assessed by comparison of pre-vaccine (2000-2005) and post-vaccine time periods (2006-2014), by age group, Indigenous status and jurisdiction using incidence rate ratios (IRR) per 100,000 population and 95% confidence intervals (CI). The national pre-vaccine notification rate in Indigenous people was four times higher than the non-Indigenous rate, and declined from 8.41 per 100,000 (95% CI 5.03-11.79) pre-vaccine to 0.85 per 100,000 (95% CI 0.00-1.99) post-vaccine, becoming similar to the non-Indigenous rate. Notification and hospitalisation rates in Indigenous children aged <5years from targeted jurisdictions declined in the post-vaccine period when compared to the pre-vaccine period (notifications: IRR=0.07; 95% CI 0.04-0.13; hospitalisations: IRR=0.04; 95% CI 0.01-0.16). As did notification rates in Indigenous people aged 5-19 (IRR=0.08; 95% CI 0.05-0.13) and 20-49years (IRR=0.06; 95% CI 0.02-0.15) in targeted jurisdictions. For non-Indigenous people from targeted jurisdictions, notification rates decreased significantly in children aged <5years (IRR 0.47; 95% CI 0.31-0.71), and significantly more overall (IRR=0.43; 95% CI 0.39-0.47) compared to non-Indigenous people from non-targeted jurisdictions (IRR=0.60; 95% CI 0.56-0.64). The national hepatitis A immunisation program has had a significant impact in the targeted population with relatively modest vaccine coverage, with evidence suggestive of substantial herd protection effects.

Investigating adverse events following immunisation with pneumococcal polysaccharide vaccine using electronic General Practice data

BACKGROUND In early 2011, following an increased number of reports of severe vaccine-related injection site reactions, Australian authorities recommended against administering repeat doses of the 23-valent pneumococcal polysaccharide vaccine (23vPPV) in otherwise healthy adults. The aim of this study was to assess a source of electronic medical record data from primary care providers (General Practitioners, GPs), for validity and ability to retrospectively detect this adverse event signal. METHODS The General Practice Research Network (GPRN) holds data routinely collected from a representative sample of Australian GPs. Data were extracted on persons 18years or older who had received at least one dose of 23vPPV or influenza vaccine (as comparator) between January 2002 and June 2012. Increases above background levels were assessed using 95% confidence intervals of reaction rates, calculated from the Poisson distribution of counts. RESULTS There was an average of 253 practices and 532 GPs contributing data per year. Over the study period there were 95,760 recorded 23vPPV administrations and 823 reactions, of which 233 were local. For influenza vaccine the numbers were 683,829 doses, 3001 and 387 respectively. Patterns of vaccinations and reactions were consistent with known safety profiles. There were 3 local reactions following 23vPPV in early 2011 (235/100,000 doses, 95% CI 49-717), which was not significantly different to the historical average (260, 225-298). We estimate that this system could have detected a 3-fold increase over background levels. CONCLUSIONS Using GP consultation data, we were unable to confirm an increase in local reactions detected by passive surveillance, suggesting that this apparent signal was artefactual. GP consultation data captures large numbers of vaccine recipients and medically attended adverse reactions at low cost. If available in a timely manner and expanded, this system has significant potential for use in validation of apparent signals from passive surveillance.