The relative effectiveness of three and four doses of COVID-19 vaccine in Victoria, Australia: A data linkage study.

BACKGROUND: The Coronavirus Disease 2019 (COVID-19) pandemic led to extensive vaccination campaigns worldwide, including in Australia. Immunity waning and the emergence of new viral variants pose challenges to the effectiveness of vaccines. Our study aimed to assess the relative effectiveness (rVE) of 3 and 4 compared with 2 doses of COVID-19 vaccine. The study focuses on the Victorian population, a majority of whom had no prior exposure to the virus before vaccination. METHODS: We used routinely collected data for the state of Victoria, Australia, to assess rVE during an Omicron-dominant period, 1 June 2022 to 1 March 2023. Immunisation, notifications, hospitalisations and mortality data for residents aged 65 years and older were linked for analysis. Cox proportional hazard regression was used to estimate the rVE against COVID-19 hospitalisation or death, accounting for key confounders with vaccination as a time-varying covariate. RESULTS: In 1,070,113 people 65 years or older who had received their second dose, a third and fourth dose of a COVID-19 vaccine significantly reduced the hazard of hospitalisation or death compared to two doses. rVE was highest within two weeks from administration at 40 % (95 % CI: 0 % to 64 %) and 66 % (95 % CI: 60 % to 71 %) for a third and fourth dose, respectively. Additional protection conferred by third and fourth doses waned over time from administration. CONCLUSIONS: Our findings underscore the need for additional vaccine doses and updated vaccine strategies. These findings have implications for public health advice and COVID-19 vaccine strategies. Further research and monitoring of vaccine effectiveness in real-world settings are warranted to inform ongoing pandemic response efforts.

Excess mortality among people with communicable diseases over a 30-year period, Victoria, Australia: a whole of population cohort study.

Background: Understanding mortality burden associated with communicable diseases is key to informing resource allocation, disease prevention and control efforts, and evaluating public health interventions. We quantified excess mortality among people notified with communicable diseases in Victoria, Australia. Methods: Cases of communicable disease notified in Victoria between 1 January 1991 and 31 December 2021 were linked to the death registry. Informational gain obtained through linkage and 30-day case fatality rates were calculated for each disease. Standardised mortality ratios (SMR) and 95% confidence intervals were calculated up to a year following illness onset. Findings: There were 1,032,619 cases and 5985 (0.58%) died ≤30 days of illness onset. Following linkage, the 30-day case fatality rate increased more than 2-fold. Diseases with high 7-day SMR signifying excess mortality included invasive pneumococcal disease (167.7, 95% CI 153.4-182.7); listeriosis (166.2, 95% CI 121.2-218.3); invasive meningococcal disease (145.9, 95% CI 116.7-178.3); legionellosis (43.3, 95% CI 28.0-62.0); and COVID-19 (21.9, 95% CI 19.7-24.3). Most diseases exhibited a strong negative gradient, with high SMRs in the first 7-days of illness onset that reduced over time. Interpretation: We demonstrated that the rate of death in Victoria's notifiable disease surveillance dataset is underestimated. Further, compared to a general population, there is evidence of elevated all-cause mortality among people notified with communicable diseases often up to one year following illness onset. Not all elevated risk is likely directly attributable to the communicable diseases of interest, rather, it may reflect underlying comorbidities or behaviours in these individuals. Regardless of attribution, infection with communicable diseases may represent a marker of mortality. Key to preventing deaths may be through timely and appropriate transition to primary and preventive healthcare following diagnosis. Funding: No funding was provided for this study.

Associations between COVID-19 and hospitalisation with respiratory and non-respiratory conditions: a record linkage study.

OBJECTIVES: To assess associations between SARS-CoV-2 infection and the incidence of hospitalisation with selected respiratory and non-respiratory conditions in a largely SARS-CoV-2 vaccine-naïve population . DESIGN, SETTING, PARTICIPANTS: Self-control case series; analysis of population-wide surveillance and administrative data for all laboratory-confirmed COVID-19 cases notified to the Victorian Department of Health (onset, 23 January 2020 - 31 May 2021; ie, prior to widespread vaccination rollout) and linked hospital admissions data (admission dates to 30 September 2021). MAIN OUTCOME MEASURES: Hospitalisation of people with acute COVID-19; incidence rate ratios (IRRs) comparing incidence of hospitalisations with defined conditions (including cardiac, cerebrovascular, venous thrombo-embolic, coagulative, and renal disorders) from three days before to within 89 days of onset of COVID-19 with incidence during baseline period (60-365 days prior to COVID-19 onset). RESULTS: A total of 20 594 COVID-19 cases were notified; 2992 people (14.5%) were hospitalised with COVID-19. The incidence of hospitalisation within 89 days of onset of COVID-19 was higher than during the baseline period for several conditions, including myocarditis and pericarditis (IRR, 14.8; 95% CI, 3.2-68.3), thrombocytopenia (IRR, 7.4; 95% CI, 4.4-12.5), pulmonary embolism (IRR, 6.4; 95% CI, 3.6-11.4), acute myocardial infarction (IRR, 3.9; 95% CI, 2.6-5.8), and cerebral infarction (IRR, 2.3; 95% CI, 1.4-3.9). CONCLUSION: SARS-CoV-2 infection is associated with higher incidence of hospitalisation with several respiratory and non-respiratory conditions. Our findings reinforce the value of COVID-19 mitigation measures such as vaccination, and awareness of these associations should assist the clinical management of people with histories of SARS-CoV-2 infection.

Maternal Vaccination and Infant Influenza and Pertussis.

BACKGROUND AND OBJECTIVES: Infant influenza and pertussis disease causes considerable morbidity and mortality worldwide. We examined the effectiveness of maternal influenza and pertussis vaccines in preventing these diseases in infants. METHODS: This inception cohort study comprised women whose pregnancies ended between September 1, 2015, and December 31, 2017, in Victoria, Australia. Maternal vaccination status was sourced from the Victorian Perinatal Data Collection and linked to 5 data sets to ascertain infant outcomes and vaccination. The primary outcome of interest was laboratory-confirmed influenza or pertussis disease in infants aged <2 months, 2 to <6 months, and <6 months combined. Secondary outcomes included infant hospitalization (emergency presentation or admission) and death. Risk ratios and 95% confidence intervals (CIs) were estimated by Poisson regression. Vaccine effectiveness (VE) was estimated as (1 minus the risk ratio) x 100%. RESULTS: Among 186 962 pregnant women, 85 830 (45.9%) and 128 060 (68.5%) were vaccinated against influenza and pertussis, respectively. There were 175 and 51 infants with laboratory-confirmed influenza and pertussis disease, respectively. Influenza VE was 56.1% (95% CI, 23.3% to 74.9%) for infants aged <2 months and 35.7% (2.2% to 57.7%) for infants aged 2 to <6 months. Pertussis VE was 80.1% (95% CI, 37.1% to 93.7%) for infants aged <2 months and 31.8% (95% CI, -39.1% to 66.6%) for infants aged 2 to <6 months. CONCLUSIONS: Our study provides evidence of the direct effectiveness of maternal influenza and pertussis vaccination in preventing these diseases in infants aged <2 months. The findings strengthen the importance of maternal vaccination to prevent these diseases in infants.

Changes in infection-related hospitalizations in children following pandemic restrictions: an interrupted time-series analysis of total population data.

BACKGROUND: Infectious diseases are a leading cause of hospitalization during childhood. The various mitigation strategies implemented to control the coronavirus disease (COVID-19) pandemic could have additional, unintended benefits for limiting the spread of other infectious diseases and their associated burden on the health care system. METHODS: We conducted an interrupted time-series analysis using population-wide hospitalization data for the state of Victoria, Australia. Infection-related hospitalizations for children and adolescents (aged <18 years, total source population ∼1.4 million) were extracted using pre-defined International Classification of Diseases 10th Revision Australian Modification (ICD-10-AM) codes. The change in weekly hospitalization rates (incidence rate ratio, IRR) for all infections following the introduction of pandemic-related restrictions from 15 March 2020 was estimated. RESULTS: Over 2015-19, the mean annual incidence of hospitalization with infection among children less than 18 years was 37 per 1000 population. There was an estimated 65% (95% CI 62-67%) reduction in the incidence of overall infection-related hospitalizations associated with the introduction of pandemic restrictions. The reduction was most marked in younger children (at least 66% in those less than 5 years of age) and for lower respiratory tract infections (relative reduction 85%, 95% CI 85-86%). CONCLUSIONS: The wider impacts of pandemic mitigation strategies on non-COVID-19 infection-related hospitalizations are poorly understood. We observed marked and rapid decreases in hospitalized childhood infection. In tandem with broader consequences, sustainable measures, such as improved hand hygiene, could reduce the burden of severe childhood infection post-pandemic and the social and economic costs of hospitalization.

Influenza and pertussis vaccination of women during pregnancy in Victoria, 2015-2017.

OBJECTIVES: To assess variations by time of year and hospital in the uptake of influenza and pertussis vaccinations by pregnant women in Victoria; to identify factors associated with vaccination uptake. DESIGN, SETTING: Retrospective analysis of data in the Victorian Perinatal Data Collection (VPDC), a population surveillance system for obstetric conditions, procedures, and pregnancy and birth outcomes. PARTICIPANTS: Women whose pregnancies ended in a live or stillbirth during July 2015 - June 2017. MAIN OUTCOME MEASURES: Influenza and pertussis vaccinations during pregnancy. RESULTS: 153 980 pregnancies in 67 hospitals ended during July 2015 - June 2017; 59 968 pregnant women (39.0%) were vaccinated against influenza and 98 583 (64.0%) against pertussis. Coverage varied by pregnancy end date, rising for influenza during winter and spring, but for pertussis rising continuously across the two years from 37.5% to 82.2%. Differences between hospitals in coverage were marked. Factors associated with vaccination included greater maternal age, primigravidity, early antenatal care, and GP-led care. The odds of vaccination were statistically significantly lower for women born overseas and those who smoked during pregnancy; the odds of vaccination were also lower for Aboriginal and Torres Strait Islander women. CONCLUSIONS: Pertussis vaccination of pregnant women in Victoria has increased, but influenza vaccination rates remain moderate and variable. Structural changes at the system level may improve maternal vaccination rates. Embedding the delivery of maternal vaccination programs in antenatal care pathways should be a priority.

Use of data linkage to improve communicable disease surveillance and control in Australia: existing practices, barriers and enablers.

OBJECTIVES: To review the use of data linkage by Australian state and territory communicable disease control units, and to identify barriers to and enablers of data linkage to inform communicable disease surveillance and control activities. METHODS: Semi-structured telephone interviews were carried out with one key informant from communicable disease control units in all eight Australian states and territories between October 2017 and January 2018. RESULTS: Key informants from all Australian states and territories participated in the interview. A variety of existing practices were identified, with few jurisdictions making systematic use of available data linkage infrastructure. Key barriers identified from the review included: a lack of perceived need; system factors; and resources. Existing regulatory tools enable data linkage to enhance communicable disease surveillance and control. CONCLUSIONS: We identified considerable variation in the use of data linkage to inform communicable disease surveillance and control activities between jurisdictions. We suggest that routinely collected, disparate data are systematically integrated into existing surveillance and response policy cycle to improve communicable disease prevention and control efforts. Implications for public health: Existing gaps in communicable disease surveillance data may affect prevention and control efforts. Data linkage is recognised as a valuable method to close surveillance gaps and should be used to enhance the value of publicly held health data.

The Rise of Imported Dengue Infections in Victoria, Australia, 2010⁻2016.

Dengue notifications have increased dramatically over the past seven years in Victoria, Australia-a trend which has been seen nationally and reflects increased cases internationally. We reviewed the epidemiology of dengue among Victorian travellers, changes in diagnostic methods and describe the burden placed on local health systems resulting from this disease of public health importance. Cases of dengue notified to the Department of Health and Human Services in Victoria, Australia, between 1 January 2010 and 31 December 2016 were included in this review. Demographic, clinical, diagnostic methods, and risk factor data were examined using descriptive epidemiological analyses. Cases of dengue increased on average by 22% per year, with a total of 2187 cases (5.5 cases/100,000 population) notified over the 7-year reporting period. The most frequently reported country of acquisition was Indonesia (45%) followed by Thailand (14%). The use of multiple diagnostic methods, including the non-structural protein 1 antigen (NS1Ag) detection test, increased over time. The median time between onset of illness and diagnosis diminished from 9 days (IQR: 2⁻15) in 2010 to 4 days (IQR: 2⁻7) in 2016. Proportionally more cases were discharged directly from emergency departments in recent years (10% in 2010 to 28% in 2016, p < 0.001).The increasing incidence of dengue in Australia is reflective of its growing prominence as a travel medicine problem in western countries. For travellers with non-severe dengue, the improved timeliness of dengue diagnostics allows for consideration of best practice ambulatory management approaches as used in endemic areas.

Effectiveness of parental cocooning as a vaccination strategy to prevent pertussis infection in infants: A case-control study.

BACKGROUND: During a pertussis epidemic in 2009, the Department of Health, Victoria, Australia, implemented a cocoon program offering parents of new babies a funded-dose of pertussis-containing vaccine. We assessed vaccine effectiveness (VE) of the program in reducing pertussis infection in infants. METHODS: Using a matched case-control design, infants aged <12 months that were notified with pertussis between 1 January 2010 and 31 December 2011, and born during the time that the cocoon program was in place, were identified. Controls were matched by area of residence and date of birth. Telephone interviews we conducted to ascertain parents' vaccination status, and if vaccinated, timing of vaccination receipt relative to the birth of their baby. Odds ratios (ORs) were calculated for the association between vaccination and pertussis infection, with VE calculated as (1 - OR) × 100%. RESULTS: The study recruited 215 cases and 240 controls (response rates 67% and 25% of eligible participants, respectively). Vaccination of both parents after delivery of the infant and ≥28 days prior to illness onset reduced pertussis infection by 77% (Vaccine Effectiveness [VE] = 77% (confidence interval [95% CI], 18-93%). After adjusting for maternal education, presence of a sibling within the household, and the infants' primary course vaccination status, the adjusted VE was 64% (95% CI, -58-92%). CONCLUSIONS: Although not reaching statistical significance, our results demonstrated that cocoon immunisation - where both parents are vaccinated in the post-partum period - may offer some protection again infant pertussis infection. Cocoon immunisation could be considered in circumstances where antenatal vaccination of the mother has not occurred.

Using data linkage to improve the completeness of Aboriginal and Torres Strait Islander status in communicable disease notifications in Victoria.

OBJECTIVE: The burden of notifiable diseases in Aboriginal and Torres Strait Islander Victorians cannot be accurately estimated due to under-reporting of Indigenous status. We used data linkage to improve completeness of Indigenous status in people notified with viral hepatitis and gonococcal infection. METHODS: Notifications made between 2009 and 2010 were linked with Victorian hospitalisation data (1997-2011). Notification rates by Indigenous status and rate ratios were calculated before and after linkage. RESULTS: There were 12,448 cases of hepatitis B, hepatitis C and gonococcal infection notified in Victoria in 2009-2010, with Indigenous status missing in 61.6%, 67.8%, 33.1% of these conditions, respectively. Of the total notified cases, 82% were able to be linked. Following linkage, the proportion of notifications with missing Indigenous status decreased to less than 0.2% for all conditions. Age-standardised notification rates among both Aboriginal people and non-Aboriginal people increased for all conditions. CONCLUSIONS: Data linkage improved completeness of Indigenous status in notifications for viral hepatitis and gonococcal infection in Victoria. Completeness of these data is integral to monitoring progress in closing the Indigenous life expectancy gap. IMPLICATIONS: Greater emphasis is needed on addressing prevention, treatment and care for viral hepatitis and sexually transmissible infections for Indigenous Victorians.

Uptake of a government-funded pertussis-containing booster vaccination program for parents of new babies in Victoria, Australia.

INTRODUCTION: An epidemic of Bordetella pertussis in Victoria, Australia, led to the implementation of a Government-funded vaccination program for parents of new babies. The rationale was to protect unimmunised infants from infection by vaccinating parents with a pertussis-containing vaccine. This is known as cocooning. AIM: To estimate uptake of the vaccine among parents of new babies, two-and-a-half years after the program was implemented. METHODS: A state-wide cross-sectional survey of parents was conducted to ascertain vaccine uptake, and to identify where and when the vaccination took place. Surveys were administered between 15 February and 14 March 2012, inclusive. RESULTS: Of 6308 surveys distributed, 2510 completed surveys were returned (response rate 40%). Ninety-five surveys completed outside the study period were excluded, leaving 2415 available for analysis. Overall, 1937 (80%) mothers and 1385 (70%) fathers were vaccinated in relation to the birth of their most recent child. A majority of mothers were vaccinated in hospital (62%). Most fathers were vaccinated by a general practitioner (72%). The most common point at which mothers were vaccinated was before their child turned two weeks of age (65%). Fathers' vaccination time-point varied more widely: during pregnancy (25%); before their child turned two weeks of age (29%); and when their child was between two and eight weeks of age (28%). CONCLUSION: Results of this survey indicated excellent uptake of the vaccine among both mothers and fathers under the Government-funded cocooning program. The findings are suggestive of an effective communications program designed to raise awareness of the risks of pertussis, and to promote availability of the funded vaccination program. The results may contribute to policy implementation of adult immunisation programs such as cocooning.

A cross sectional survey of attitudes, awareness and uptake of the parental pertussis booster vaccine as part of a cocooning strategy, Victoria, Australia.

BACKGROUND: The Victorian Government Department of Health funded a diphtheria, tetanus and acellular pertussis vaccine for parents of infants from June 2009 to June 2012 as part of a cocooning strategy for the control of pertussis. The aim of this study was to assess parents' attitudes and awareness of the vaccination program, and to estimate vaccine uptake. METHODS: A cross-sectional survey of 253 families with a child born in the first quarter of 2010 residing within five metropolitan and four rural local government areas in Victoria was conducted. Univariate analyses were performed to describe the relationship between demographic variables, knowledge and awareness of the disease, the vaccine program and vaccine uptake. Multivariate analyses examining predictors for awareness of the vaccine program and for the uptake of vaccination were also conducted. RESULTS: One hundred and five families were surveyed (response rate 43%). Of these, 93% indicated that they had heard of 'pertussis' or 'whooping cough' and 75% of mothers and 69% of fathers were aware the pertussis vaccine was available and funded for new parents. Overall, 70% of mothers and 53% of fathers were vaccinated following their child's birth, with metropolitan fathers less likely to be vaccinated as rural fathers (RR=0.6, p=0.002). Being a younger mother (p=0.02) or father (p=0.047), and being an Australian-born father (RR=1.9, p=0.03) were found to predict uptake of the vaccine in parents. CONCLUSION: Parents indicated a reasonable level of knowledge of pertussis and a willingness to be vaccinated to protect their child. However, vaccine uptake estimates indicated further opportunity for program improvement. Future cocooning strategies would benefit from specifically targeting fathers and metropolitan maternity hospitals to increase vaccine uptake. Wider promotion of the availability of vaccine providers may increase uptake to maximise the success of cocooning programs. Further investigation of the effectiveness of the cocooning strategy in decreasing infant morbidity and mortality is required.

Evaluation of Campylobacter infection surveillance in Victoria.

Campylobacter infection is a notifiable infectious disease in Victoria and with more than 6,000 cases notified annually, it is the second most commonly notified disease after chlamydia. The objectives of Campylobacter infection surveillance in Victoria are to monitor the epidemiology of Campylobacter infection, identify outbreaks, initiate control and prevention actions, educate the public in disease prevention, evaluate control and prevention measures, and plan services and priority setting. An evaluation of the system was undertaken to assess performance against its objectives, identify areas requiring improvement and inform a decision of whether Campylobacter infection should remain a notifiable infectious disease. The surveillance system was assessed on the attributes of data quality, timeliness, simplicity and acceptability using notifiable infectious diseases data and interviews with doctors who had failed to notify, and laboratory and public health staff. The evaluation found that the system collects core demographic data with high completeness that are appropriately reviewed, analysed and reported. In 2007, 12% of Campylobacter isolates were subtyped and only one to 3 outbreaks were identified annually from 2002 to 2007. Fifty-four per cent of cases were notified by doctors and 96% by laboratories, although nearly half of laboratory notifications were not received within the prescribed timeframe. Half of the surveyed non-notifying doctors thought that Campylobacter infection was not serious enough to warrant notification. The Campylobacter surveillance system is not fully satisfying its objectives. Investment in the further development of analytical methods, electronic notification and Campylobacter subtyping is required to improve simplicity, acceptability, timeliness and sensitivity.

Hepatitis a outbreak epidemiologically linked to a food handler in Melbourne, Victoria.

Hepatitis A is caused by the hepatitis A virus (HAV). Transmission occurs by the faecal-oral route, either by direct contact with an HAV-infected person or by ingestion of HAV-contaminated food or water. Hepatitis A outbreaks are uncommon in Australia. In 2008, Victoria experienced an outbreak of hepatitis A due to an infected food handler.