Assessing the Impact of Pneumococcal Conjugate Vaccine Immunization Schedule Change From 3+0 to 2+1 in Australian Children: A Retrospective Observational Study.

BACKGROUND: In mid-2018, the Australian childhood 13-valent pneumococcal conjugate vaccine schedule changed from 3+0 to 2+1, moving the third dose to 12 months of age, to address increasing breakthrough cases of invasive pneumococcal disease (IPD), predominantly in children aged >12 months. This study assessed the impact of this change using national IPD surveillance data. METHODS: Pre- and postschedule change 3-dose 13-valent pneumococcal conjugate vaccine breakthrough cases were compared by age group, serotype, and clinical syndrome. Annual rates of breakthrough cases were calculated (per 100 000) using respective birth cohort sizes and 3-dose vaccine coverage. Using time-series modelling, observed IPD rates in children aged <12 years were compared to that expected if the 3+0 schedule were continued. FINDINGS: Over 2012-2022, rate of 3-dose breakthrough cases in children aged >12 months was 2.8 per 100 000 (n = 557; 11 birth cohorts). Serotype 3 replaced 19A as predominant breakthrough serotype (respectively, 24% and 65% in 2013 to 60% and 20% in 2022) followed by 19F. In breakthrough cases, the most frequent clinical phenotype was bacteremic pneumonia (69%), with meningitis accounting for 3%-4%. In cohorts eligible for 2+1 versus 3+0 schedules, rate of breakthrough cases was lower for all vaccine serotypes, except type 3 (incidence rate ratio, 0.50 [95% confidence interval, .28-.84] and 1.12 [0.71-1.76], respectively). Observed compared to expected IPD was 51.7% lower (95% confidence interval, -60.9 to -40.7%) for vaccine serotypes, but the change for nonvaccine types was not significant 12% (-9.6 to 39.7). INTERPRETATIONS: The 2+1 schedule is likely superior to 3+0 for overall IPD control, a finding that may be worth consideration for other countries considering or using 3+0 PCV schedules.

ATAGI targeted review 2023: Vaccination for preventing influenza in Australia.

Abstract: Annual seasonal influenza epidemics cause substantial disease and economic burden worldwide. During the coronavirus disease 2019 (COVID-19) pandemic in 2020 and 2021, influenza activity significantly declined. However, influenza resurged in Australia following the relaxation of non-pharmaceutical interventions, with increased influenza virus circulation in early 2022 coinciding with the SARS-CoV-2 Omicron BA.2 variant wave. Together with other respiratory virus diseases, these disease impacts on the Australian population and healthcare system have re-emphasised the importance of influenza vaccination and control. We aim to provide an overview of the current seasonal influenza vaccination program in Australia and summarise evidence and considerations underpinning potential future immunisation strategies. Influenza causes disproportionately higher morbidity and mortality in young children and older adults. Other populations at elevated risk from influenza include Aboriginal and Torres Strait Islander peoples, pregnant women, and people with certain underlying medical conditions. All Australians aged ≥ 6 months are recommended to receive influenza vaccine every year. The National Immunisation Program (NIP) provides free vaccine for eligible at-risk populations. While approximately 70% of older adults had received influenza vaccine in 2022, coverage in other age groups remains suboptimal. There are several key unmet needs and challenges, but also potential strategies for enhancing the influenza vaccination program in Australia. Improved monitoring and evaluation, including the use of relevant linked datasets for such purposes, is imperative to better understand variations in coverage and vaccination impact in specific populations. Adoption of evidence-based strategies, such as culturally appropriate resources that consider the characteristics of diverse Australian populations, may also help to achieve higher vaccine coverage rates. Additionally, greater vaccine uptake across the population could be facilitated by expanding the NIP-eligible population where cost-effective, and adopting the use of more effective and different types of vaccines when available.

Real-world utilisation of SARS-CoV-2 rapid antigen testing to enable face-to-face learning in Australian schools, an ecological study.

OBJECTIVE: The objective of this study was to describe the use of SARS-CoV-2 rapid antigen testing of COVID-19 contacts in New South Wales schools to determine return to in-person school attendance instead of home quarantine, between 6 November and 21 December 2021. METHODS: COVID-19 school contacts were required to quarantine for two weeks postexposure to the case. Students who opted into daily rapid antigen testing logged their results in a database, prior to school attendance, and obtained SARS-CoV-2 nucleic amplification acid testing on day 12-16. Secondary attack rates (SARs) in schools utilising rapid antigen testing (Test-to-Stay schools) and those not utilising rapid antigen testing (non-Test-to-Stay school) were calculated. RESULTS: We identified 9,887 people in 293 schools who reported performing at least one rapid antigen test (RAT). The SAR in RAT schools was 3.4% (95% confidence interval: 2.7-4.1) and non-RAT schools was 2.8% (95% confidence interval: 2.4-3.3). A total of 30,535 school days were preserved through this program. CONCLUSIONS: The use of RATs preserved in-person learning without a significant increase to SAR. IMPLICATION FOR PUBLIC HEALTH: Disruptions in face-to-face learning have long-term detrimental impacts on children and adolescents. Rapid antigen testing has been shown to be beneficial to maintain face-to-face learning in Australian schools and may be a useful method to safeguard from school disruptions in future pandemics.

Surveillance of adverse events following immunisation in Australia, COVID-19 vaccines, 2021.

Abstract: This report summarises Australia's spontaneous (passive) surveillance data for adverse events following immunisation (AEFI) for coronavirus disease 2019 (COVID-19) vaccines in 2021 reported to the Therapeutic Goods Administration (TGA). The TGA strongly promoted and facilitated adverse event reporting in preparation for, and during, the COVID-19 vaccine rollout as a core component of the most intensive vaccine safety monitoring ever conducted in Australia. There were 111,348 AEFI reports for COVID-19 vaccines administered in 2021, an annual AEFI reporting rate of 271.4 per 100,000 doses of COVID-19 vaccines administered to people aged ≥ 12 years. The annual AEFI reporting rate for non-COVID-19 vaccines in 2021 was 30.6 per 100,000 doses administered to people of all ages. Overall, the most frequently reported symptoms were headache, adverse events classified as 'gastrointestinal nonspecific symptoms and therapeutic procedures', myalgia, pyrexia and fatigue, which were consistent with common expected adverse events following COVID-19 vaccines used in Australia. The most commonly reported adverse events of special interest were myocarditis and/or pericarditis, followed by thrombosis and thromboembolism, and anaphylaxis. Of all COVID-19 vaccine AEFI reports, 762 (0.7%) included a fatal outcome, of which over 80% were in people aged ≥ 60 years. Thirteen deaths reported in 2021 were assessed as likely to be causally linked to vaccination. This report confirms the value of spontaneous post-marketing vaccine pharmacovigilance, especially in the context of new vaccines using novel vaccine technologies and near whole-of-population pandemic vaccination programs. The most frequently reported AEFI for COVID-19 vaccines were common, mild and temporary (lasting 1 or 2 days), and consistent with clinical trial and active surveillance data. Ongoing safety monitoring detected rare, unexpected conditions, such as myocarditis/pericarditis and thrombosis with thrombocytopenia syndrome (TTS), which were investigated and confirmed as safety signals, resulting in changes to vaccine recommendations and product information. The outcomes of TGA monitoring were published in weekly vaccine safety reports. Overall, COVID-19 vaccine safety monitoring provided critical information on the risks of vaccine related adverse events that enabled decisionmakers to undertake informed risk-benefit assessments.

Surveillance of adverse events following immunisation in Australia annual report, 2021.

Abstract: This report summarises Australia's spontaneous surveillance data for adverse events following immunisation (AEFI) for 2021 reported to the Therapeutic Goods Administration (TGA) and describes reporting trends over the 22-year period 1 January 2000 to 31 December 2021. This report excludes AEFI reports featuring pandemic coronavirus disease 2019 (COVID-19) vaccines, which are reported separately. There were 3,452 AEFI reports for non-COVID-19 vaccines administered in 2021, an annual AEFI reporting rate of 13.4 per 100,000 population compared with 14.9 per 100,000 population in 2020. This small decrease in the AEFI reporting rate in 2021 could potentially be related to an increased focus on COVID-19 vaccines and related AEFI, which are not included in this report. AEFI reporting rates for individual vaccines in 2021 were similar to 2020, as were the most commonly reported adverse events. Of the six deaths following vaccination in 2021 reported to the TGA, none were found to have a causal relationship with vaccination.

Australian vaccine preventable disease epidemiological review series: Hepatitis B, 2000-2019.

Introduction: Hepatitis B vaccination was nationally funded for adolescents in 1996, with inclusion of universal infant immunisation under the National Immunisation Program (NIP) in May 2000. This study describes hepatitis B epidemiology in Australia in the two decades since 2000. Methods: This article analyses newly-acquired (within the prior 24 months) and unspecified (all other) hepatitis B notifications (2000-2019) from the National Notifiable Diseases Surveillance System; acute hepatitis B hospitalisations (2001-2019) from the National Hospital Morbidity Database; and acute (2000-2019) and chronic (2006-2019) hepatitis B deaths from the Australian Bureau of Statistics and Australian Coordinating Registry. Rates over the reporting period were described overall, and by age group, sex, and Aboriginal and Torres Strait Islander status (Aboriginal and/or Torres Strait Islander versus other [neither Aboriginal nor Torres Strait Islander, unknown or not stated]). Trend analyses were performed using Poisson or negative binomial regression. Additional analyses were performed for the cohort born after May 2000. Results and discussion: The annual all-age notification rate per 100,000 per year declined (p < 0.001) from 2.13 in 2000 to 0.65 in 2019 for newly-acquired hepatitis B and from 38.3 to 22.3 for unspecified hepatitis B (likely to predominantly represent chronic hepatitis B). Newly-acquired and unspecified hepatitis B notification rates were lowest among children aged < 15 years. The most substantial reductions in notification rates of newly-acquired hepatitis B were among adolescents aged 15-19 years and young adults aged 20-24 and 25-29 years (respectively 17-, 11-, and 7-fold); these age groups also recorded the most substantial reductions in unspecified hepatitis B notifications (respectively 5-, 3.5-, and 2-fold). Newly-acquired hepatitis B notification and acute hepatitis B mortality rates were two- to threefold higher in males than females. The all-age newly-acquired hepatitis B notification rate in Aboriginal and Torres Strait Islander people decreased twofold between 2000 and 2019, but remained threefold higher than in other people. Acute hepatitis B hospitalisations also declined over the study period (p < 0.001) and followed similar patterns. There were no acute or chronic hepatitis B deaths among people born after May 2000; this cohort featured 52 newly-acquired and 887 unspecified hepatitis B notifications. Due to lack of data on country of birth (and hence eligibility for infant vaccination under the NIP or overseas programs), vaccination status and likely transmission routes, we were unable to assess factors contributing to these potentially preventable infections. Conclusion: Adolescent and infant immunisation under the NIP has led to significant reductions in notification rates of newly-acquired hepatitis B, and in acute hepatitis B hospitalisation rates, both overall and in Aboriginal and Torres Strait Islander people. Unspecified hepatitis B notification rates have also greatly decreased in children and young adults, likely largely due to the impact of overseas infant immunisation programs on prevalence in child and adolescent migrants. Work to improve completeness of variables within national datasets is crucial, along with enhanced surveillance of both newly-acquired and unspecified hepatitis B cases to investigate transmission routes, vaccination status and factors contributing to acquisition of hepatitis B, in order to optimise the impact of immunisation programs and ensure linkage with care.

The seroprevalence of antibodies to Japanese encephalitis virus in five New South Wales towns at high risk of infection, 2022: a cross-sectional serosurvey.

OBJECTIVES: To determine the proportion of people in New South Wales towns at high risk of Japanese encephalitis virus (JEV) infections during the 2022 outbreak; to identify risk factors for JEV infection. STUDY DESIGN: Cross-sectional serosurvey study of the seroprevalence of JEV-specific antibodies in NSW. SETTING, PARTICIPANTS: Convenience sample of people (all ages) from five regional NSW towns deemed to be at high risk of JEV infections after first outbreak of Japanese encephalitis in southeastern Australia in early 2022 (Balranald, Corowa, Dubbo, Griffith, Temora), 21 June - 22 July 2022. MAIN OUTCOME MEASURES: Proportion of people seropositive for JEV total antibody, assayed by defined epitope-blocking enzyme-linked immunosorbent assay; prevalence odds ratios for exposure risk factors and protective behaviours. RESULTS: Eighty of 917 eligible participants (559 girls or women, 61%; 42 Aboriginal and Torres Strait Islander people, 4.6%; median age, 52 years [IQR, 37-62 years]) were seropositive for JEV-specific total antibody (8.7%); the median age of seropositive people was 61 years (IQR, 48-70 years). The seropositivity proportion was largest for people aged 65 years or more (30 of 192; weighted proportion, 13.7%) and larger for male than female participants (30 of 358, 10.6% v 50 of 559, 7.5%). Five of 42 samples from Aboriginal and Torres Strait Islander participants were seropositive (12%). We found mixed associations with a range of potential risk factors. CONCLUSION: We found evidence for a substantial number of JEV infections in five regional NSW towns during a single arbovirus season in 2022. Public health responses, including effective surveillance, vaccination against JEV, and mosquito management, are critical for controlling outbreaks. Promoting behaviours that reduce exposure to mosquitoes is a core component of prevention, particularly when the vaccine supply is limited.

Serosurvey for Japanese encephalitis virus antibodies following an outbreak in an immunologically naïve population, Victoria, 2022: a cross-sectional study.

OBJECTIVES: To investigate the distribution and prevalence of Japanese encephalitis virus (JEV) antibody (as evidence of past infection) in northern Victoria following the 2022 Japanese encephalitis outbreak, seeking to identify groups of people at particular risk of infection; to investigate the distribution and prevalence of antibodies to two related flaviviruses, Murray Valley encephalitis virus (MVEV) and West Nile virus Kunjin subtype (KUNV). STUDY DESIGN: Cross-sectional serosurvey (part of a national JEV serosurveillance program). SETTING: Three northern Victorian local public health units (Ovens Murray, Goulburn Valley, Loddon Mallee), 8 August - 1 December 2022. PARTICIPANTS: People opportunistically recruited at pathology collection centres and by targeted recruitment through community outreach and advertisements. People vaccinated against or who had been diagnosed with Japanese encephalitis were ineligible for participation, as were those born in countries where JEV is endemic. MAIN OUTCOME MEASURES: Seroprevalence of JEV IgG antibody, overall and by selected factors of interest (occupations, water body exposure, recreational activities and locations, exposure to animals, protective measures). RESULTS: 813 participants were recruited (median age, 59 years [interquartile range, 42-69 years]; 496 female [61%]); 27 were JEV IgG-seropositive (3.3%; 95% confidence interval [CI], 2.2-4.8%) (median age, 73 years [interquartile range, 63-78 years]; 13 female [48%]); none were IgM-seropositive. JEV IgG-seropositive participants were identified at all recruitment locations, including those without identified cases of Japanese encephalitis. The only risk factors associated with JEV IgG-seropositivity were age (per year: prevalence odds ratio [POR], 1.07; 95% CI, 1.03-1.10) and exposure to feral pigs (POR, 21; 95% CI, 1.7-190). The seroprevalence of antibody to MVEV was 3.0% (95% CI, 1.9-4.5%; 23 of 760 participants), and of KUNV antibody 3.3% (95% CI, 2.1-4.8%; 25 of 761). CONCLUSIONS: People living in northern Victoria are vulnerable to future JEV infection, but few risk factors are consistently associated with infection. Additional prevention strategies, including expanding vaccine eligibility, may be required to protect people in this region from Japanese encephalitis.

Assessing the effects of SARS-CoV-2 vaccination on the risk of household transmission during delta variant circulation: a population-based data linkage cohort study.

Background: Data on SARS-CoV-2 vaccine effectiveness to reduce transmission of infection in household settings are limited. We examined the effects of SARS-CoV-2 vaccines on Delta variant transmission within households in an infection-naïve population. Methods: This was a population-based data linkage cohort study in the Greater Sydney Metropolitan Area, New South Wales, Australia based on cases observed in June-November 2021. In households with ≥1 confirmed COVID-19 case, we calculated adjusted odds ratios (aOR) and 95% Confidence Intervals (95% CI) for the risk of SARS-CoV-2 transmission, by vaccination status (unvaccinated, partially vaccinated, fully vaccinated, or waning) and type of vaccines (mRNA or vector-based) received by both index cases and household contacts. Findings: In 20,651 households with a single index case, 18,542 of 72,768 (25%) household contacts tested PCR-positive ≤14 days after their respective index case. Household contacts with partial, full, or waning mRNA vaccination had aORs of 0.46 (95% CI 0.40-0.52), 0.36 (95% CI 0.32-0.41) and 0.64 (95% CI 0.51-0.80) compared to unvaccinated contacts, while for vector vaccines the corresponding aORs were 0.77 (95% CI 0.67-0.89), 0.65 (95% CI 0.55-0.76), and 0.64 (95% CI 0.39-1.05). Full mRNA-vaccination in index cases compared to non-vaccination was associated with aORs between 0.09 and 0.21 depending on the vaccination status of household contacts. Interpretation: Full vaccination of household contacts reduced the odds to acquire infection with the SARS-CoV-2 Delta variant in household settings by two thirds for mRNA vaccines and by one third for vector vaccines. For index cases, being fully vaccinated with an mRNA vaccine reduced the odds of onwards transmission by four-fifths compared to unvaccinated index cases. Full vaccination offered stronger protection than partial vaccination, particularly for mRNA vaccines, but with reduced effects when the last vaccination preceded exposure by ≥3 months. Funding: New South Wales Ministry of Health.

Seroprevalence of Japanese encephalitis virus-specific antibodies in Australia following novel epidemic spread: protocol for a national cross-sectional study.

INTRODUCTION: Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus that causes encephalitis and other morbidity in Southeast Asia. Since February 2022, geographically dispersed JEV human, animal and vector detections occurred on the Australian mainland for the first time. This study will determine the prevalence of JEV-specific antibodies in human blood with a focus on populations at high risk of JEV exposure and determine risk factors associated with JEV seropositivity by location, age, occupation and other factors. METHOD: Samples are collected using two approaches: from routine blood donors (4153 samples), and active collections targeting high-risk populations (convenience sampling). Consent-based sampling for the latter includes a participant questionnaire on demographic, vaccination and exposure data. Samples are tested for JEV-specific total antibody using a defined epitope-blocking ELISA, and total antibody to Australian endemic flaviviruses Murray Valley encephalitis and Kunjin viruses. ANALYSIS: Two analytic approaches will occur: descriptive estimates of seroprevalence and multivariable logistic regression using Bayesian hierarchical models. Descriptive analyses will include unadjusted analysis of raw data with exclusions for JEV-endemic country of birth, travel to JEV-endemic countries, prior JEV-vaccination, and sex-standardised and age-standardised analyses. Multivariable logistic regression will determine which risk factors are associated with JEV seropositivity likely due to recent transmission within Australia and the relative contribution of each factor when accounting for effects within the model. ETHICS: National Mutual Acceptance ethical approval was obtained from the Sydney Children's Hospitals Network Human Research Ethics Committee (HREC). Local approvals were sought in each jurisdiction. Ethical approval was also obtained from the Australian Red Cross Lifeblood HREC. DISSEMINATION: Findings will be communicated to participants and their communities, and human and animal health stakeholders and policy-makers iteratively and after final analyses. Understanding human infection rates will inform procurement and targeted allocation of limited JEV vaccine, and public health strategies and communication campaigns, to at-risk populations.

Effectiveness of bivalent COVID-19 boosters against COVID-19 mortality in people aged 65 years and older, Australia, November 2022 to May 2023.

We followed 4,081,257 Australian adults aged ≥ 65 years between November 2022 and May 2023 for COVID-19-specific mortality, when recombinant SARS-CoV-2 Omicron lineages (predominantly XB and XBB) as well as BA.2.75 were circulating. Compared with a COVID-19 booster targeting ancestral SARS-CoV-2 given > 180 days earlier, the relative vaccine effectiveness against COVID-19 death of a bivalent (ancestral/BA.1 or ancestral/BA.4-5) booster given 8 to 90 days earlier was 66.0% (95%CI: 57.6 to 72.2%) and that of a monovalent ancestral booster given 8 to 90 days earlier was 44.7% (95%CI: 23.9 to 59.7%).

Superior immunogenicity of mRNA over adenoviral vectored COVID-19 vaccines reflects B cell dynamics independent of anti-vector immunity: Implications for future pandemic vaccines.

Both vector and mRNA vaccines were an important part of the response to the COVID-19 pandemic and may be required in future outbreaks and pandemics. The aim of this study was to validate whether immunogenicity differs for adenoviral vectored (AdV) versus mRNA vaccines against SARS-CoV-2, and to investigate how anti-vector immunity and B cell dynamics modulate immunogenicity. We enrolled SARS-CoV-2 infection-naïve health care workers who had received two doses of either AdV AZD1222 (n = 184) or mRNA BNT162b2 vaccine (n = 274) between April and October 2021. Blood was collected at least once, 10-48 days after vaccine dose 2 for antibody and B cell analyses. Median ages were 42 and 39 years, for AdV and mRNA vaccinees, respectively. Surrogate virus neutralization test (sVNT) and spike binding antibody titres were a median of 4.2 and 2.2 times lower, respectively, for AdV compared to mRNA vaccinees (p < 0.001). Median percentages of memory B cells that recognized fluorescent-tagged spike and RBD were 2.9 and 8.3 times lower, respectively for AdV compared to mRNA vaccinees. Titres of IgG reactive with human adenovirus type 5 hexon protein rose a median of 2.2-fold after AdV vaccination but were not correlated with anti-spike antibody titres. Together the results show that mRNA induced substantially more sVNT antibody than AdV vaccine, which reflected greater B cell expansion and targeting of the RBD rather than an attenuating effect of anti-vector antibodies. ClinicalTrials.gov Identifier: NCT05110911.

Summary of National Surveillance Data on Vaccine Preventable Diseases in Australia, 2016-2018 Final Report.

Erratum Two tables within this report, as originally published, contained errors which are notified and corrected here.

ATAGI 2023 Annual Statement on Immunisation.

The Australian Technical Advisory Group on Immunisation (ATAGI) 2023 Annual Statement on Immunisation is the third publication in this series. It highlights the key successes, trends and challenges in the use of vaccines and control of vaccine preventable diseases (VPDs) in Australia in 2022. It also signals ATAGI's priority actions for addressing key issues for 2023 and beyond.

Annual immunisation coverage report 2021.

Introduction: We analysed Australian Immunisation Register (AIR) data as at 3 April 2022 for children, adolescents and adults for the calendar year 2021, with data on trends from previous years also presented. Children: 'Fully vaccinated' coverage in Australian children in 2021 was 0.6-0.8 of a percentage point lower than in 2020 at the 12-month (94.2%) and 60-month (94.0%) age assessment milestones, but stable at the 24-month milestone (92.1%). Due to the lag time involved in assessment at milestone ages, 'fully vaccinated' coverage figures for 2020 and 2021 predominantly reflect vaccinations due in 2019 and 2020, respectively, and hence show a small impact on childhood coverage in the first year of the coronavirus disease 2019 (COVID-19) pandemic. 'Fully vaccinated' coverage in Aboriginal and Torres Strait Islander (hereafter respectfully referred to as Indigenous) children was 0.7-1.5 percentage points lower in 2021 than 2020 at the 12-month (91.6%), 24-month (90.1%) and 60-month (96.3%) milestones, although 2.3 percentage points higher than children overall at 60 months. Influenza vaccination coverage in children aged 6-59 months was approximately 20 percentage points lower in 2021 than 2020, both for children overall (26.5%) and for Indigenous children (22.5%). 'On time' vaccination (within 30 days of the recommended age) was up to two percentage points lower in 2021 than 2020 for vaccines due at 4 and 6 months of age, suggesting possible pandemic impacts, but was similar or higher for vaccines due at 12 months of age. While on-time vaccination in Indigenous children has improved progressively since 2012, it remained 6-13 percentage points lower than in children overall in 2021. 'Fully vaccinated' coverage at the earlier milestones (3 months after due date of last scheduled vaccine) of 9, 15, 21 and 51 months was 1.5-2.8 percentage points lower for children living in the least advantaged residential area quintile than the most advantaged, a similar disparity as in 2020. Coverage at the earlier milestones was 2.3-10.0 percentage points lower for Indigenous children living in remote areas than in major cities and regional areas, with disparity at 21 months of age 2.1-2.2 percentage points higher in 2021 than in 2020, and 1.2-2.1 percentage points higher at 51 months. Adolescents: In 2021, a total of 80.3% of girls and 77.2% of boys (and 73.3% and 66.2% of Indigenous girls and boys) had completed the human papillomavirus (HPV) vaccination schedule by 15 years of age, 0.2-0.4 of a percentage point lower than 2020 (1.7-1.8 percentage points for Indigenous), reflecting vaccinations due in school programs prior to the pandemic with possible pandemic impact on catch-up vaccination. However, the proportion of adolescents completing the two-dose HPV vaccination schedule within a calendar year was 15.3 percentage points lower in 2021 than 2020 and 26.9 percentage points lower than in 2019, likely due to pandemic-related disruption to school-based programs. Additionally, 87.3% of adolescents (83.8% for Indigenous) had received the recommended booster dose of diphtheria-tetanus-acellular pertussis (dTpa) vaccine by 15 years, and 76.1% (66.7% for Indigenous) the recommended meningococcal ACWY vaccine dose by 17 years of age. Adults: Zoster vaccine coverage in 2021 remained relatively low, at just over 30%, in adults aged 70 years, but increased to 47% in those aged 71-79 years, reflecting ongoing catch-up vaccination. Coverage of 13vPCV was low in 2021, reaching 17.2% in adults aged 70 years and 20.1% in those aged 71-79 years. Influenza vaccination coverage in adults in 2021 was progressively higher with increasing age, reaching 62.1% in the 65-74 years age group (64.6% in Indigenous) and 68.5% in the 75+ years age group (67.7% in Indigenous). Influenza vaccine coverage for other National Immunisation Program (NIP)-eligible Indigenous adult age groups was only 22.0% for those aged 20-49 years, and 43.5% for those aged 50-64 years. By the end of 2021, a total of 91.6% of people in Australia aged 16+ years had received a second dose of a COVID-19 vaccine (71.8% for Indigenous), with over 99% of those aged 70+ years having received a second dose. Conclusions: Vaccination coverage in children and adolescents remained relatively high in 2021, although with some evidence of COVID-19 pandemic impacts, particularly on receipt of two doses of HPV vaccine within the same calendar year. It will be important to ensure catch-up vaccination in children and adolescents occurs. A strengthened focus on adult vaccination is needed, as coverage remained suboptimal in 2021. The impact of mandatory reporting of all NIP vaccinations from mid-2021, on completeness of AIR data, has not yet been formally evaluated.

Effectiveness of COVID-19 vaccination against COVID-19 specific and all-cause mortality in older Australians: a population based study.

Background: Few studies have examined effectiveness of COVID-19 vaccines against COVID-19 and all-cause mortality across different pandemic periods in 2022. Methods: We used linked whole-of-population data from the 2021 Australian Census, Australian Immunisation Register, death registrations and other national datasets including migration data. Among 3.8 million adults aged 65+ years and >170,000 aged care residents, we used survival analysis to estimate vaccine effectiveness (VE) against COVID-19 specific mortality and all-cause mortality, by vaccine dose and time since receipt, adjusted for age, sex and other factors. We also estimated absolute COVID-19 mortality rates. Findings: From January-May 2022 (Omicron BA.1/2), 3250 COVID-19 deaths occurred; from June-November (Omicron BA.4/5) 3185 COVID-19 deaths occurred. During January-May, VE of a 3rd COVID-19 vaccine dose within 3 months was 93% (95% CI 93-94%) whilst VE of a 2nd dose >6 months since receipt was 34% (26-42%). During June-November, VE of a 4th COVID-19 vaccine dose within 3 months was 84% (82-86%) whilst VE of a 3rd dose >6 months since receipt was 56% (50-62%). VE estimates for aged care residents were similar, but absolute risk reductions were substantially greater. During June-November 2022, for all-cause mortality, VE of a 4th dose within 3 months was 58% (56-59%) whilst VE of a 3rd dose >6 months since receipt was 19% (16-22%). Interpretations: COVID-19 vaccination is highly effective against COVID-19 mortality among older adults although effectiveness wanes with time since the last dose. Our findings emphasise the importance of continuing to administer booster doses, particularly to those at highest risk. Funding: This study was funded by the Health Economics Research Division in the Australian Government Department of Health and Aged Care.

The clinicopathological features of thrombosis with thrombocytopenia syndrome following ChAdOx1-S (AZD1222) vaccination and case outcomes in Australia: a population-based study.

Background: Thrombosis with thrombocytopenia syndrome (TTS) associated with viral vector COVID-19 vaccines, including ChAdOx1-S (AstraZeneca AZD1222) vaccine, can result in significant morbidity and mortality. We report the clinicopathological features of TTS following ChAdOx1-S vaccination and summarise the case outcomes in Australia. Methods: In this cohort study, patients diagnosed with TTS in Australia between 23 March and 31 December 2021 were identified according to predefined criteria. Cases were included if they met the Therapeutic Goods Administration (TGA) probable and confirmed case definitions and were reclassified using Centres for Disease Control and Prevention (CDC) definition for analysis. Data were collected on patient baseline characteristics, clinicopathological features, risk factors, treatment and outcomes. Findings: A total of 170 TTS cases were identified, with most occurring after the first dose (87%) of ChAdOx1-S. The median time to symptom onset after vaccination and symptom onset to admission was 11 and 2 days respectively. The median age of cases was 66 years (interquartile range 55-74). All except two patients received therapeutic anticoagulation and 66% received intravenous immunoglobulin. Overall, 85.3% of cases were discharged home after a median hospitalisation of 6 days, 9.4% required ongoing rehabilitation and 5.3% died. Eight deaths were related to TTS, with another dying from an unrelated condition while receiving treatment for TTS. Deaths occurred more commonly in those classified as Tier 1 according to the CDC definition and were associated with more severe thrombocytopenia and disease-related haemorrhage. Interpretation: TTS, while rare, can be severe and have catastrophic outcomes in some individuals. In Australia, the mortality rate was low compared to that reported in other high-income countries. Almost all received therapeutic anticoagulation with no bleeding complications and were successfully discharged. This emphasises the importance of community education and an established pathway for early recognition, diagnosis and treatment of TTS. Funding: Australian Commonwealth Department of Health and Aged Care. H.A Tran, N. Wood, J. Buttery, N.W. Crawford, S.D. Chunilal, V.M. Chen are supported by Medical Research Future Funds (MRFF) grant ID 2015305.