Obesity linked to COVID-19 severity in children during pre-Omicron wave

A recent study has found that individuals with obesity had more severe COVID-19 during the ancestral and pre-Omicron waves, but not during the Omicron wave.

“Importantly, the same phenomenon was observed in unvaccinated children, suggesting that differences in vaccination did not account for the observed changes in the need for respiratory support over time,” the researchers said.

A total of 6,176 polymerase chain reaction-confirmed SARS-CoV-2 infected children and adolescence (aged 2 <18 years) from Australia, Brazil, Italy, Portugal, Switzerland, Thailand, the UK, and the US hospitalized between 1 January 2020 and 31 March 2022.

The researchers collected data across three time periods representing dominant SARS-CoV-2 variants: the ancestral strain (T1), pre-Omicron variants (Alpha and Delta; T2), and Omicron (T3). The need for supplemental oxygen therapy or ventilatory/respiratory support was the main outcome.

The median age of participants was 11.0 years, and 2,989 (48.4 percent) were female. Some 5,460 (88.4 percent) children had available obesity status, of whom 213 (3.9 percent) met the criteria for having obesity. [Pediatr Infec Dis J 2025;44:1084-1093]

Obesity showed a positive association with the need for respiratory support during T1 (risk ratio [RR], 3.45, 95 percent confidence interval [CI], 2.02‒5.88) and T2 (RR, 3.24, 95 percent CI, 1.57‒6.67), but not during T3 (RR, 3.08, 95 percent CI, 0.85‒11.15). Similar findings were seen for unvaccinated children.

“Consistent with these previous studies, the analysis performed herein noted a significant association between obesity and the need for respiratory support during the earlier stages of the pandemic but not during the Omicron wave,” the researchers said.

Vaccination

The findings could have been influenced by vaccination efforts against COVID-19 among children with obesity during the Omicron period, which provided protection against severe disease. [J Korean Med Sci 2023;38:e65]

“However, our large dataset inclusive of children hospitalized in eight countries does not support this,” the researchers said. “Namely, no association between obesity and respiratory support was observed during the Omicron wave when only unvaccinated children were included in the analysis.”

Additionally, if this were the case, one would expect that children with other comorbidities would also no longer be at elevated risk during the Omicron wave, according to the researchers. “In this study, pre-existing neurological disease and asthma remained as risk factors for increased respiratory support during the Omicron wave.”

Previous reports supported these data that children with neurological disease remained at increased risk of severe COVID-19 during the said period despite vaccination. [J Korean Med Sci 2023;38:e65]

“The question, therefore, remains why obesity was not a clear statistically significant risk factor for children during the Omicron wave of the pandemic,” the researchers said. “It is possible that these data reflect genetic changes in the Omicron variant that dramatically altered the pathogenesis of the virus.”

Another possible explanation is the protective effect of previous infection. Children with obesity may have had a greater risk of infection with SARS-CoV-2 than other children, as shown in other respiratory pathogens. [Sci Adv 2024;10:eadk9137; Influenza Other Respir Viruses 2019;13:3-9]

“Thus, by the time the Omicron wave emerged, children with obesity had sufficient levels of prior immunity that the deleterious effect of obesity on COVID-19 outcomes was reduced,” the researchers said.