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Abstract
Background The clinical course of Australian children admitted to hospital with COVID-19 infection is not well understood, particularly over the Omicron period.
Methods This study describes paediatric admissions to a single tertiary paediatric institution through the Delta and Omicron variant waves. All children admitted from 1 June 2021 to 30 September 2022 with a diagnosis of COVID-19 infection were included for analysis.
Results 117 patients were admitted during the Delta wave compared with 737 during the Omicron wave. The median length of stay was 3.3 days (IQR 1.7–6.75.1) during Delta, compared with 2.1 days (IQR 1.1–3.4) during Omicron (p<0.01). 83 patients (9.7%) required intensive care unit (ICU) admission, a greater proportion during Delta (20, 17.1%) than Omicron (63, 8.6%, p<0.01). Patients admitted to the ICU were less likely to have received a dose of COVID-19 vaccination prior to admission than patients admitted to the ward (8, 24.2% vs 154, 45.8%, p=0.028).
Conclusion The Omicron wave resulted in an absolute increase in the number of children compared with Delta, but cases had lower severity, demonstrated by shorter length of stay and a smaller proportion of patients requiring intensive care. This is consistent with US and UK data describing a similar pattern.
- COVID-19
- virology
Data availability statement
All data relevant to the study are included in the article or uploaded as supplemental information.
This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.
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WHAT IS ALREADY KNOWN ON THIS TOPIC
Overall, children have mild or asymptomatic COVID-19 compared with adults. More children were admitted to hospital with COVID-19 infection during the Omicron compared with the Delta wave.
WHAT THIS STUDY ADDS
Vaccinated children appear to be less likely to require intensive care. Almost 40% of children admitted with COVID-19 had comorbidities. Comorbidities were more common in the adolescent cohort.
HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY
Hospitals and clinicians are better able to understand at-risk groups for hospital admission from COVID-19-positive infections, and to alter practice or policy to preferentially protect these groups through measures such as immunisation.
Introduction
The clinical course of Australian children admitted to hospital with COVID-19 infection caused by recent SARS-CoV-2 variants following the original Wuhan strain is not well understood. Consistent with international experience from the USA and UK, Australian data have demonstrated overall mild disease in paediatric patients during the Delta wave, and an increase in admissions in the Omicron wave compared with preceding variants.1–3
We describe paediatric admissions to a tertiary paediatric institution through the Delta (B.1.617.1) and Omicron (B.1.1.529, BA.2, BA.3, BA.4, BA.5) variant waves, the two most dominant variants in Australia during the study period.
Methods
We identified children aged up to 18 years admitted to a tertiary paediatric hospital in Victoria, Australia, between 1 June 2021 and 30 September 2022 with a primary or secondary diagnosis of COVID-19 using the hospital electronic medical record (Epic Systems, Verona, Wisconsin, USA). Based on epidemiological patterns, 22 December 2021 was identified as the transition when Omicron became predominant in Victoria. Admissions before this date were classified as the ‘Delta’ period, and after as ‘Omicron’.
Patients admitted to an inpatient ward were included for analysis (excluding emergency department and Hospital in the Home presentations, and those admitted solely for COVID-19 therapeutic infusions such as sotrovimab, who did not otherwise require admission). Pearson’s Χ2 test was applied for comparing categorical variables and Mann-Whitney U test for continuous variables. Logistic regression adjusted for sex was used to assess the association between age and comorbidities, as well as being overweight. The statistical programming language R was used for analyses. A p value of <0.05 was considered statistically significant.
Patient and public involvement
The research question and outcome measures were informed by patient priorities and experience as established in institutional experience and feedback related to COVID-19, including the organisation National Child Health Poll. Given the retrospective design of the study, patients were not involved in recruitment or conduct of the study. Population and cohort results from the study will be available via public forums to all patients and staff of our organisation.
Results
All children admitted to the hospital were tested for COVID-19 infection. Eight hundred fifty-four admitted children had a positive SARS-CoV-2 test. The majority of patients (657, 76.9%) were admitted for the primary reason of COVID-19 infection, with the remainder for an incidental finding of COVID-19 during an admission for another reason. Of these, 190 (22.2%) were <6 months old, 295 (34.5%) 0.5–4 years, 188 (22.0%) 5–11 years and 181 (21.2%) were 12–18 years old with a median age of 3 years (IQR: 0.6–10). One hundred seventeen patients were admitted during the Delta wave (1 June 2021–21 December 2021) compared with 737 during the Omicron wave (22 December 2021–30 September 2022, figure 1) with the peak number of weekly admissions being 14 for Delta and 53 for Omicron. There was one death (during the Delta period) in a child with significant immunocompromise and other comorbidities.
COVID-19 positive hospital admissions by week.
The median length of stay was 3.3 days (IQR 1.7–6.7) during Delta, compared with 2.1 days (IQR 1.1–4.5) during Omicron (Mann-Whitney U test: p<0.01) (figure 2). Seven hundred ten (83.1%) patients did not require any respiratory support during their admission.
Length of stay of COVID-19 admissions by variant.
Three hundred forty patients (39.8%) had a pre-existing comorbidity. Furthermore, a sex-adjusted logistic regression indicated that comorbidities is associated with age (p<0.001). Patients with comorbidities had a higher median age of 6 years (IQR: 2–13) compared with 1.5 years (IQR: 0.3–8) in those without any comorbidities. This was further reflected when comparing adolescents (≤12 years) with those <12 years old. Here, adolescents had a comparatively higher rate of underlying comorbidities (103, 56.9% vs 237, 35.2%, Pearson’s Χ2 test: p<0.001). Similarly, this age group was more often overweight (weight >90th centile (54, 29.8% vs 146, 21.7%), Pearson’s Χ2 test: p=0.028) than the younger age group. This trend was further reflected through a sex-adjusted logistic regression showing that age in general is significantly associated with being overweight (p<0.001) with the median age for overweight patients being 6 years (IQR: 2–12) compared with 2 years (IQR: 0.5–10) for those with a weight below the 90th percentile (figure 3).
COVID-19 positive hospital admission by age and weight. BMI, body mass index; ICU, intensive care unit.
Eighty-three patients (9.7%) required intensive care unit (ICU) admission, a greater proportion during Delta (20, 17.1%) than Omicron (63, 8.6%, Pearson’s Χ2 test: p<0.01). Furthermore, 63 patients (7.4%) required invasive respiratory support (high-flow nasal therapy, continuous positive airway pressure, bilevel positive airway pressure or mechanical ventilation), with a trend towards greater requirements during Delta (14, 12.0%) than Omicron (49, 6.7%, Pearson’s Χ2 test: p=0.064) (figure 4B). Interestingly, there were also differences between age groups regarding the type of respiratory support required, with a peak in the 6 months–4 years (not eligible for vaccination) and the adolescent age group (Pearson’s Χ2 test: p=0.035) (figure 4A).
A) COVID-19 positive hospital admissions by respiratory support - by age group B) by SARS-COV-2 strain. IV, invasive ventilation; NIV, non-invasive ventilation.
Just under half of patients (369 cases) were eligible for vaccination at the time of their COVID-19 infection. One hundred sixty-two patients had at least one dose of vaccination prior to admission. Of these, fewer patients admitted to the ICU had at least one dose of COVID-19 vaccination prior to admission compared with patients admitted to the ward (8, 24.2% vs 154, 45.8%, Pearson’s Χ2 test: p=0.028).
Discussion
The Omicron wave resulted in an absolute increase in the number of children admitted to a single tertiary institution compared with Delta, but cases had lower severity, demonstrated by shorter length of stay and a smaller proportion of patients requiring intensive care and respiratory support. In particular, vaccinated children appear to be less likely to require intensive care. This is consistent with US and UK data describing a similar pattern.2 3
Given that this is a single-centre experience, care needs to be taken when generalising these results to other centres, including the consideration of other contributing factors to decreasing severity in the Omicron wave.
Data availability statement
All data relevant to the study are included in the article or uploaded as supplemental information.
Ethics statements
Patient consent for publication
Ethics approval
The study was approved by the hospital Human Research Ethics Committee (HREC #64003 and #38301).
Footnotes
Contributors DRC conceptualised and designed the study, drafted the initial manuscript, assisted with data collection and analysis, and critically reviewed and revised the manuscript. SS and AM collected data, carried out the analyses, and critically reviewed and revised the manuscript. NWC, ST and SM critically reviewed and revised the manuscript. ACS conceptualised the study, and critically reviewed and revised the manuscript. All authors approved the final manuscript as submitted and agree to be accountable for all aspects of the work, with ACS acting as guarantor for the study.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
Provenance and peer review Not commissioned; externally peer reviewed.