Hospitalisations and deaths following COVID-19, 2020–2022: a linked data analysis

People diagnosed with COVID-19

More than 1 in 3 Australians (8.5 million) had a COVID-19 notification by 31 December 2022 recorded in the Register (which excludes Western Australia). Focusing only on people with a COVID-19 notification:

• around 26,900 (0.3%) were diagnosed before the Delta wave (25 January 2020 to 15 June 2021)
• around 203,000 (2.4%) were diagnosed during the Delta wave (16 June 2021 to 14 December 2021)
• around 8.2 million (97.3%) were diagnosed during the Omicron period (15 December 2021 to 31 December 2022).

Prior to Omicron, 1 in 100 people experienced COVID-19 compared to more than 1 in 3 people from the start of Omicron to the end of 2022. While the Omicron variant was more transmissible, its emergence also coincided with the relaxation of a number of public health measures following attainment of high rates of vaccine coverage in the population.

The term COVID-19 ‘diagnosis’ in this report refers to people with at least one COVID-19 notification reported to state and territory notifiable disease registers. It includes people diagnosed using nucleic acid amplification testing (for example, reverse transcription polymerase chain reaction) or Rapid Antigen Tests (Interim Australian Centre for Disease Control 2024).

The number of people per capita with a COVID-19 diagnosis varied across Australia (Figure 1) and was:

• highest in Victoria and New South Wales during the first 2 years prior to the Omicron period
• highest in the Australian Capital Territory, Tasmania and South Australia during Omicron (to the end of 2022)
• higher in young adult to middle-aged groups (ranging from 41% to 44% aged 10–49) compared with children (29% aged 0–9) and people aged 70–89 (23%)
• higher for females (39% of all females) compared to males (34%). This difference was greater in the young adult and middle-aged groups (for example, 47% of females compared with 37% of males, aged 20–29)
• highest among people living in Major cities and lowest among residents in Remote and very remote areas – 38% compared with 21%
• comparable across socioeconomic groups during the Omicron wave, however socioeconomic disparities were pronounced in earlier waves. Prior to Omicron, COVID-19 diagnoses were 2.4 times as high in the lowest group (18 per 1,000 people) compared to the highest (7 per 1,000).

Notes:

1. People are counted in each wave based on their first reported COVID-19 diagnosis date.
2. Total includes people with missing data on sex but excludes people with missing information on age/remoteness area/socioeconomic group. Total for state/territory breakdown includes people usually resident in Western Australia and Other Territories notified through participating jurisdictions and people with missing geographical data.

See Data tables to access downloadable tables containing data on people with COVID-19 as shown in Figure 1.

Subsequent notified infections (reinfections)

In this report, a subsequent notified SARS-CoV-2 infection (or reinfection) is defined as more than 90 days between two positive tests in accordance with international studies (CDC 2023, COVID-19 Forecasting Team 2023, Yahav D et al. 2021). Due to data availability, it only includes subsequent infections that were notified to state and territory health officials. This is likely an underestimate of the true number of reinfections. See the Technical notes for more information.

Overall, 4.8% of people with a COVID-19 notification had a reinfection by the end of 2022.

COVID-19 reinfections:

• were highest among females (5.4%) and young adults aged 20–29 (7.4%).
• declined with increasing geographical remoteness, from 4.9% in Major cities to 3.3% of residents in Remote and very remote areas.
• declined with increasing socioeconomic group, from 5.3% for the lowest group to 4.5% for the highest group.

See Data tables to access downloadable tables containing re-infection data.