COVID-19 Australia: Epidemiology Report 75

Reporting period ending 4 June 2023

Abstract

Four-week reporting period (8 May – 4 June 2023)

Case definitions for confirmed and probable cases are in accordance with the coronavirus disease 2019 (COVID-19) Series of National Guidelines for Public Health Units (SoNG).

Trends – Nationally, there has been a gradual increase in case notifications since early March 2023, reflecting the start of a fifth wave of Omicron transmission. In the four-week period 8 May – 4 June 2023, there were 42,489 confirmed and 107,526 probable cases of COVID-19 reported in Australia to the National Notifiable Diseases Surveillance System (NNDSS). In the most recent reporting fortnight, a total of 71,374 confirmed and probable cases were notified (an average of 5,098 cases per day), compared to 78,641 in the previous fortnight (an average of 5,617 cases per day).

Age group – Since the start of the fifth Omicron wave in early March 2023, there has been an overall increase in notification rates across all age groups. However, in the most recent fortnight (ending 4 June 2023) notification rates have started to stabilise across all age groups. In the current reporting period 8 May – 4 June 2023, the highest notification rate was observed among adults aged 90 years and over, whilst the lowest rates were among children aged nine years or less. For the entire Omicron wave to date (15 December 2021 – 4 June 2023), the highest notification rate has been in adults aged 20 to 29 years.

Aboriginal and Torres Strait Islander people – In the reporting period 8 May – 4 June 2023, there were 4,292 new cases notified in Aboriginal and Torres Strait Islander people. In the Omicron wave to date (15 December 2021 – 4 June 2023), there have been 416,207 cases notified among Aboriginal and Torres Strait Islander people, representing 3.7% (416,207/11,230,206) of all cases during this period.

Severity – Since the start of the fifth Omicron wave, there has been a slight increase in the number of cases with severe illness (defined as those admitted to ICU or died), however notifications of severe cases have remained considerably lower than in previous Omicron waves. The overall crude case fatality rate since the start of the fifth Omicron wave is 0.40%, which is higher than the fourth (0.34%) and third (0.21%) Omicron waves. The current case fatality rate is likely overestimated due to changes in case ascertainment and underreporting of non-severe cases. Since the start of the pandemic to 4 June 2023, there have been 177 cases of paediatric inflammatory multisystem syndrome - temporally associated with SARS-CoV-2 (PIMS-TS) reported to the Paediatric Active Enhanced Disease Surveillance network (PAEDS), with two new cases reported in the last four weeks and a total of 11 cases reported since the start of 2023.

Virology – For samples collected in the four-week period 8 May – 4 June 2023, all 2,522 samples were assigned against Omicron or recombinants consisting of Omicron lineages. There is currently significant diversity in the range of sub- and sub-sub-lineages circulating within Australia. During the reporting period, more than 200 unique lineages have been identified. Recombinant lineages represented the majority (89.8%) of sequences collected during 8 May – 4 June 2023 and available for analysis in AusTrakka. In the same period, BA.2 (now predominantly represented by the BA.2.75 sub-lineage) and BA.5 account for 10.0% and 0.2%, respectively, of sequences identified in the same period.

Acute respiratory illness – Based on self-reported FluTracking data, there has been an overall increase in the prevalence of both ‘fever and cough’ and ‘runny nose and sore throat’ symptoms in the community since late January 2023. Over the current period, the rate of ‘fever and cough’ has sharply increased but remains slightly lower than the rates observed during the same period in 2022. The rate of ‘runny nose and sore throat’ symptoms increased to 1.8% of participants with respiratory illness, exceeding the rate observed in 2022 for the same period.

International situation – According to the World Health Organization (WHO), cumulative global COVID-19 cases stood at over 767 million COVID-19 cases and over 6.9 million deaths as of 4 June 2023. For the South-East Asia and Western Pacific regions combined, there were 986,933 new cases and 2,065 deaths in the four-week period to 4 June 2023. A proportional decrease in new cases and deaths was observed in the South-East Asia (cases: -77%; deaths: -35%) and Western Pacific regions (cases: -5%; deaths: -19%) compared with the previous four weeks. In total, since the start of the pandemic, approximately 265 million cases and over 1.2 million deaths have been reported in the two regions.