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COVID-19 Australia: Epidemiology Report 55

vaccine administered in Australia. Nationally, 18,866,665 people aged 16 years or over (91.5%) had received at least one dose, including 17,550,642 people aged 16 and over (85.1%) who were fully vaccinated.


COVID-19 Australia: Epidemiology Report 55
Reporting period ending 21 November 2021 COVID-19 National Incident Room Surveillance Team Summary Trends -The daily average of 1,298 cases for this reporting period was lower than the previous fortnight's daily average of 1,528 cases. There were 18,166 cases of coronavirus disease 2019 (COVID-19) reported this fortnight, bringing the 2021 cumulative case count to 170,420 cases.
Clusters and high-risk settings -As at 21 November 2021, there had been 73,924 locally-acquired cases in New South Wales, including 567 deaths, since the first case of the Sydney Metropolitan outbreak was reported on 16 June 2021. Genomic testing showed that the outbreak's primary case was infected with the 'Delta' SARS-CoV-2 variant of concern (B.1.617.2). The fortnightly number of new locally-acquired cases reported in New South Wales continued to decrease, with 2,966 locally-acquired cases reported this reporting period, compared to 3,189 locally-acquired cases in the previous reporting period. In recent weeks, the proportion of locally-acquired cases in regional and remote residents has decreased.
As at 21 November 2021, there were 90,602 cases, including 461 deaths, associated with the Victorian outbreaks since the first cases were reported on 5 August 2021. These primary cases involved the Delta variant and were closely associated with the current New South Wales and the July 2021 Victorian outbreaks. The number of new cases in the Victorian outbreak decreased during the reporting period, with 14,922 locally-acquired cases reported this fortnight compared to 18,033 in the previous fortnight. Most new cases in the outbreak were across several parts of Greater Melbourne. The proportion of cases identified in regional and remote residents decreased this reporting period compared with the previous reporting period.
As at 21 November 2021, a total of 1,929 cases, including 11 deaths, had been reported as part of the Australian Capital Territory outbreak. The primary case in the outbreak was reported on 12 August 2021 and was infected with the Delta variant. The number of new cases in the Australian Capital Territory during this reporting period (187) was slightly higher than in the previous reporting period (145).
As at 21 November 2021, a total of 34 locally-acquired cases had been reported in the Northern Territory since 5 November 2021. These cases were part of two genomically linked clusters: an initial four cases detected in Darwin and Katherine between 5 and 10 November 2021, and 30 Surveillance summary cases detected in Katherine, Robinson River and surrounding homelands since 15 November 2021. At the end of the reporting period, there were active cases in Katherine, Robinson River and Binjari.
A total of eight locally-acquired cases was reported as part of a cluster in Goondiwindi, Queensland, with the first case reported on 4 November 2021. The first case is believed to have acquired their infection in Moree, New South Wales. The most recent cases associated with this cluster were reported on 12 November 2021.
Aboriginal and Torres Strait Islander persons -During the reporting period, there were 869 new cases notified in Aboriginal and Torres Strait Islander people, of whom 520 were from New South Wales; 290 were from Victoria; 31 were from the Northern Territory; 25 were from the Australian Capital Territory; and three were from Queensland. To date in 2021, there have been 8,384 cases and 16 deaths reported among Aboriginal and Torres Strait Islander people. Of locally-acquired cases notified in Aboriginal and Torres Strait Islander people in 2021 to date, 42% (3,487/8,384) lived in a regional or remote area.
Overseas cases -There were 51 overseas-acquired cases this reporting period, with the largest number of such cases reported in New South Wales (65%; 33/51), followed by Western Australia (16%; 8/51).
Severity -In 2021, based on the highest level of severity reported for cases with an illness onset up to 7 November 2021, 0.7% of cases were reported to have died, a further 1.2% of cases required intensive care and a further 8.4% required admission to hospital, noting that cases may be hospitalised for reasons other than clinical COVID-19 related care. Given the delay between illness onset and severe illness, cases with an onset in the last two weeks were excluded from the analysis on severity. During the reporting period, 113 new COVID-19-associated deaths were notified. This reporting period covers the two-week period 8-21 November 2021, with data for this period compared to that from the previous twoweek reporting period (25 October -7 November 2021). 1 The focus of this report is on the epidemiological situation in Australia since the beginning of 2021. Readers are encouraged to consult prior reports in this series for information on the epidemiology of cases in Australia in 2020.

Vaccinations -
Acute respiratory illness, testing, public health response measures, virology and the international situation are reported in detail on a four-weekly basis and are not included in this report. The latest information on these topics can be found in Epidemiology Report 54; 1 state and territory health websites; i the weekly situation reports of the World Health Organization (WHO); ii and the Department of Health's current situation and case numbers webpage. iii From report 46 onward, and unless otherwise specified, tabulated data and data within the text are extracted from the National Interoperable Notifiable Diseases Surveillance System (NINDSS) iv based on 'notification received date' rather than 'diagnosis date' (see the Technical Supplement for definitions). 2 As a case's diagnosis date can be several days prior to the date of its notification, there is potential for newly-notified cases to be excluded from the case count in the current reporting period when reporting by 'diagnosis date'. Using 'notification received date' ensures that the case count for the reporting period better reflects the number of newly-notified cases. As the graphs presented in this report, based on NINDSS data, reflect a larger time period (i.e. year to date and entire pandemic),   (Table 2).
In the reporting period, New South Wales reported the largest number of overseasacquired cases (65%; 33/51), followed by Western Australia (16%; 8/51) ( Table 1). In the past 28 days (25 October to 21 November 2021), twenty-three percent (16/69) of confirmed overseas-acquired cases reported to the NINDSS had an unknown country of acquisition. Cases acquired in the United Kingdom (21%; 11/53) were the most numerous of those with an identified country of acquisition in the past 28 days, followed by the United States of America (13%; 7/53).
Since May 2021, the proportion of air arrivals diagnosed with COVID-19 has remained at less than 1%. On 1 November 2021, several states changed quarantine requirements for vaccinated arrivals. Since then, there has been a substantial increase in the number of air arrivals; however, the proportion of overseas-acquired cases amongst these arrivals has remained less than 1%. The number of cases acquired in different countries is influenced by travel patterns of returning Australians, travel restrictions, and the prevalence of COVID-19 in the country of travel.

Demographic features (NINDSS)
In this reporting period, the largest proportion of cases occurred in children aged 5 to 11 years (23%; 4,182/18,166). Notification rates were also highest in people aged 5 to 11, at 183.7 per 100,000 population, over twice that of the next highest age group. For this year, the highest rate of infection has been in those aged 5 to 11 years with a rate of 959.4 infections per 100,000 population, followed by people aged 18 to 29 (927.1 per 100,000 population) ( Figure 3; Appendix A,   b The lighter bar at the right represents the most recent reporting week and should be interpreted with caution as additional cases may be identified in the coming week that have a diagnosis date during this period.
In 2021, notification rates were higher among males than females in most age groups, though rates were similar among males and females in those aged 0 to 15 years and were also similar in those over 90 years old ( Figure 3; Appendix A,     b Note, from this report, the age groups have been changed to match those used to report severity.     Clusters and outbreaks Sydney Metropolitan Outbreak and New South Wales Regional Outbreak -New South Wales In total, as at 21 November 2021, there had been 73,924 locally-acquired cases, including 567 deaths, reported in New South Wales following notification of the outbreak's first case on 16 June 2021. Genomic testing results showed that the first case was infected with the Delta SARS-CoV-2 variant of concern (B.1.617.2); however, the sequence did not match cases from the Victorian Delta variant outbreak that occurred from May to June 2021. This sequence had not been seen in Australia previously, but matched one from the United States of America.
Overall, the number of new locally-acquired cases (including cases under initial investigation) continued to decrease this fortnight, with 2,966 cases reported this reporting period, compared to 3,189 such cases reported in the previous reporting period. Following the initial start of the outbreak in south-east Sydney, the largest number of new cases were subsequently reported among residents of south-western and western Sydney, with cases also reported in residents of regional and remote areas in New South Wales, particularly in western New South Wales. In the reporting period, the proportion of locallyacquired cases in regional and remote residents decreased; 30% (897/2,966) of locally-acquired cases in NSW this reporting period were in residents of regional or remote areas, compared with 39% (1,241/3,189) in the previous reporting period. Regional areas with current outbreaks during this reporting period included the Hunter New England, Mid-North Coast and Albury-Wodonga regions.

Metropolitan Melbourne and Victorian Regional Outbreak -Victoria
As at 21 November 2021, there had been 90,602 locally-acquired cases, including 461 deaths, reported in Victoria since two unlinked cases were reported on 5 August 2021. Investigations into the source of the outbreak were ongoing, but genomic testing had determined that these outbreaks involved the Delta variant and were genomically closely associated with recent clusters in New South Wales and the previous two seeding events in Victoria from July 2021.
Overall, the number of new locally-acquired cases decreased this reporting period, with 14,922 locally-acquired cases (including cases under initial investigation) reported in Victoria this fortnight, compared to 18,033 in the previous fortnight. Most new cases in the outbreak were across several parts of Greater Melbourne. In the reporting period, the proportion of cases in regional remote residents decreased, with 11% (1,636/14,922) of locally-acquired cases reported in Victoria this reporting period being in residents of regional or remote areas, compared to 15% (2,768/18,033) in the previous reporting period.

Canberra -Australian Capital Territory
As at 21 November 2021, a total of 1,929 cases had been reported in the Australian Capital Territory's outbreak, including 11 deaths. The first case in the Territory's outbreak, which was the first locally-acquired case in the Australian Capital Territory in over a year, was reported on 12 August 2021 and was confirmed to have the Delta variant. The source of infection remained under investigation at the end of this reporting period, though it was genomically related to the Sydney Metropolitan Outbreak. The number of new locally-acquired cases (including cases under initial investigation) in the Australian Capital Territory during this reporting period (187) was higher than the number in the previous reporting period (145).

Northern Territory outbreak -Northern Territory
As at 21 November 2021, there had been 34 locally-acquired cases reported in the Northern Territory since 5 November 2021. An initial four cases were detected between 5 November and 10 November 2021, associated with a traveller from Melbourne. Exposure sites from these cases were identified in both Darwin and Katherine local government areas. A second cluster, which, as of 21 November 2021, comprised 30 locallyacquired cases in the Katherine, Robinson River and surrounding homelands, was first reported on 15 November 2021. The two clusters were genomically linked, however the epidemiological link remained under investigation. Current areas of concern at the end of this reporting period included Katherine, Robinson River and Binjari.

Goondiwindi cluster -Queensland
A total of eight locally-acquired cases was reported as part of a cluster in Goondiwindi, Queensland. The first case in the cluster was reported on 4 November 2021 and is believed to have acquired their infection in Moree, New South Wales. The most recent cases associated with this cluster were reported on 12 November 2021.

(NINDSS, SPRINT-SARI)
Hospitalisation and intensive care unit admission Given the delay between illness onset and severe illness, to provide a more accurate assessment of the highest level of severity, cases with an onset in the last two weeks were excluded from the analysis. In 2021, based on the highest level of severity reported for cases with an illness onset up to 7 November 2021, 0.7% of cases were reported to have died; a further 1.2% of cases required intensive care; and a further 8.4% required admission to hospital ( Table 6). Note that hospitalisation data in NINDSS should be interpreted with caution: hospitalisation is not always reflective of severe illness, as cases may be hospitalised for reasons other than clinical

Risk factors for severe disease
The proportion of cases who were admitted to hospital generally increased as a person's age increased (Table 6).
Comorbidity data extracted from SPRINT-SARI reflect the sickest patients with COVID-19 managed in ICU; data are therefore not generalisable to all cases (Table 7). In patients admitted to ICU with COVID-19 since 1 February 2021, the most prevalent comorbidity was obesity (a body mass index of > 30 or weight over 120 kg), followed by diabetes. Of those adult patients admitted to ICU this year for whom comorbidity data was known, 64% (1,043/1,629) had at least one comorbidity; 36% (586/1,629) of patients had none of the listed comorbidities recorded.

COVID-19 deaths
In the past two weeks, there were 113 deaths associated with COVID-19: ninety-two in Victoria and 21 in New South Wales. This brings the total number of COVID-19-associated deaths in 2021 to 1,058 (Table 8). c From this report, the age groups have been changed to match those used to report severity.