The 23-month-old died at Queensland Children's Hospital on Sunday night, but the death was only confirmed late on Tuesday.

"The death of a child is awfully sad," Deputy Premier Steven Miles told reporters on Wednesday.

"My heart just goes out to that family, and of course to our health workers who would have done everything that they could to take care of that little child."

Mr Miles said there were about 1000 people in hospital with COVID-19 in Queensland, but there are no plans to reintroduce a mask mandate or any other health measures to suppress the outbreak.

"Now that everyone has had a chance to get vaccinated, we have a different set of responses and measures and you can see the effectiveness of that vaccination in the hospitalisation rates," he said.

Hospitalisations as a proportion of case numbers were much lower than earlier variants, he said.

"The number of those hospitalisations who are needing ICU care is lower and the number of fatal cases as a proportion of total cases is also lower."

Meanwhile, almost half of adult Australians are estimated to have contracted COVID-19 since the pandemic began in early 2020.

Sydney's Kirby Institute says 46.2 per cent of adults were estimated to have had the virus by early June, with more than a quarter of the population infected in the previous three-month period.

The prevalence is almost triple that reported in its previous serosurvey - an analysis of blood antibody tests - which estimated about 17 per cent of the population had been infected by late February.

"While we know there is a lot of virus circulating in the community, we can't rely on testing data alone to understand how many people have been infected," the institute's Dorothy Machalek said.

"Some may experience only mild symptoms, or none at all, and they may not always have a test to detect the virus.

"There is also high use of rapid antigen tests, which don't always get reported."

Dr Machalek said the serosurveys provide a more complete picture of how much COVID-19 is out there because they measure blood donors' antibodies to the virus, created when the immune system responds to infection, which remain present for months afterwards.

Evidence of infection was highest among donors aged between 18 and 29, at more than 61 per cent.

It dropped to about 25 per cent in donors aged between 70 and 89 in Victoria, NSW, Queensland, and Western Australia.

In Western Australia, evidence of past infections in blood donors rose rapidly over a three-month period, from 0.5 per cent to 37.5 per cent.

Chief Medical Officer Paul Kelly has said the surveys are crucial to informing the country's pandemic response.

LATEST 24-HOUR COVID-19 DATA:

* Queensland: 8209 cases, 19 deaths, 1023 in hospital with 26 in ICU

* NSW: 16,173 cases, 20 deaths, 2275 in hospital with 56 in ICU

* Victoria: 12,653 cases, 32 deaths, 872 in hospital with 33 in ICU

* Tasmania: 1313 cases, four deaths, 170 in hospital with three in ICU

* SA: 4197 cases, four deaths, 365 in hospital with eight in ICU

* WA: 5422 cases, three deaths, 442 in hospital with 17 in ICU

* ACT: 1104 cases, 141 in hospital with one in ICU

* NT: 491 cases, one death, 76 in hospital with one in ICU

Australian Associated Press