Admissions of children with COVID-19 to intensive care decreased over successive waves of the virus, according to a global study of disease severity in children across 9 countries, including Australia.
And the age of the children had an impact on COVID-19 severity.
Many studies looking at the severity of COVID-19 in children have assessed the group as a single cohort.
Publishing in JAMA Pediatrics, researchers drew on clinical data from 31,785 hospitalised children and adolescents to assess how the severity of the disease changed in different age groups between January 2020 and March 2022.
The study considers COVID-19 severity based on admissions to intensive care units (ICU) as well as oxygen and ventilation support in three age groupings: children younger than 6 months, 6 months to 5 years and 5 to 18 years.
Data was analysed from 9 countries including: Australia, Brazil, Italy, Portugal, South Africa, Switzerland, Thailand, the United Kingdom and the United States.
The data from each country reflects three specific time periods as different COVID-19 variants came to the fore. The first reflecting hospitalisations when the initial strain of COVID-19 dominated, the second where pre-Omicron variants of concern were common, and the third when Omicron-derived variants of concern prevailed.
Overall, the data shows 8.6% of all children hospitalised were admitted to ICU, 16.4% required oxygen support and 3.5% required ventilation support. More boys than girls were admitted to hospital with COVID-19 across each time period.
For children aged 5 to 18, ICU admissions declined over successive COVID-19 periods, along with the need for ventilation and oxygen support. The study notes that those results remained consistent when the data was limited to unvaccinated children.
While ICU admissions also decreased over time for children aged 6 months to 5 years, the use of ventilation and oxygen support did not.
For children younger than 6 months, ICU admissions and ventilation support decreased over time, and the use of oxygen support did not.
Reduced ICU admissions over time may reflect the protective effect of prior infection, functional changes in the virus, or changes in healthcare, the paper says.
The findings highlight the importance of considering different age groups in children when assessing the severity of COVID-19 as well as in public health responses.