Most children with cancer have asymptomatic or mild disease with a COVID-19 infection, but more than one in ten have severe or critical disease and require prolonged ICU admission, new research shows.

In a multinational study of 131 children from 10 countries including Australia, the children aged 4-14 years were mostly on active treatment for haematological (60%) or solid cancers (37%) or primary immunodeficiency and HSCT (3%).

COVID-19 disease severity was categorised as asymptomatic in 32%, mild in 47%, moderate in 8%, severe in 4%, and critical in 9% of the children.

“On multivariate analysis, comorbidity, any coinfection and neutropenia remained independently and significantly associated with increasing disease severity,” the study said.

The study, published in the European Journal of Cancer, found no difference in the proportion of patients with symptomatic infection who were on active cancer treatment (69%) or who had completed treatment (65%).

Half of the children were admitted to hospital at the time of infection, including 37% for COVID-19 related symptoms or management and 12% for chemotherapy or other non-COVID-19 related treatment.

The median length of hospital stay was 9.3 days, 15 patients (11%) required ICU admission, and four (3%) died due to COVID-19 while one died due to disease progression.

“Notably, more than one-third of patients on active treatment had chemotherapy interruptions due to COVID-19, including cycles withheld in 30%, which may impact treatment response and risk of relapse.”

Mortality was higher in patients who had completed cancer treatment or had undergone HSCT (13%) compared with patients on active treatment (0.9%).

“This observation is in contrast to adult patients, where patients on systemic anticancer therapy had a similar risk of death to patients on no treatment.”

“Factors such as increasing age, comorbidities and potentially a protective effect of corticosteroids in children on active treatment are some hypotheses that may explain these results.”

The study found the median duration from known SARS-CoV-2 exposure to earliest onset of symptoms or positive PCR result for asymptomatic cases was 5 days.

The median duration of virus detection by PCR was 16 days in the 51 patients with two or more positive respiratory swabs.

The study authors said although vaccination of children has commenced in some regions, there is no data on vaccine efficacy in the paediatric cancer population, and clinical studies are urgently needed.