Infectious Disease

Omicron more infectious, less severe than delta for young children

April 07, 2022

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Young children were more likely to be infected with the omicron variant than the delta variant of SARS-CoV-2 but less likely to experience severe health outcomes, researchers reported in JAMA Pediatrics.

“The omicron variant is highly infectious in children,” co-author Rong Xu, PhD, a professor of biomedical informatics and founding director of the Center for Artificial Intelligence in Drug Discovery at Case Western Reserve School of Medicine, told Healio. “While it may be less severe than the delta variant, its associated severe clinical outcomes are still substantial.”

Young children were more likely to be infected with the omicron variant than the delta variant of SARS-CoV-2 but less likely to experience severe health outcomes, according to researchers. Source: Adobe Stock.

Rong Xu

Xu and colleagues analyzed the health records of 651,640 children aged younger than 5 years in the United States not yet eligible for COVID-19 vaccination who had medical encounters with health care organizations between September 2021 and January 2022.

The patients were divided into three cohorts: 22,772 children in the omicron cohort infected between Dec. 26, 2021, and Jan 25, 2022; 66,692 in the delta cohort infected between Sept. 1 and Nov. 15, 2021; and 10,492 children in the delta2 cohort infected between Nov. 16 and 30, 2021.

The monthly incidence rate of COVID-19 infections was mostly stable (1 to 1.5 cases per 1,000 persons per day) during the delta-predominant period between September and November 2021, but increased rapidly during the emergence of the omicron variant in December 2021 (2.4 to 5.6 cases per 1,000 persons per day).

Further demographic data analysis found that children infected with omicron were on average younger and had fewer comorbidities compared with those in the delta cohort, although these differences were eliminated after matching.

Children in the omicron cohort were less likely to visit the ED compared with those in the delta (HR = 0.84; 95% CI, 0.8-0.87) and delta2 cohorts (HR = 1.06; 95% CI, 1-1.12). They also were less likely to be hospitalized (HR = 0.66; 95% CI, 0.58-0.74 and HR = 1.07; 95% CI, 0.93-1.24), admitted to the ICU (HR = 0.35; 95% CI, 0.25-0.51 and HR = 0.74; 95% CI, 0.49-1.11) or receive mechanical ventilation (HR = 0.15; 95% CI, 0.07-0.33 and HR = 1.08; 95% CI, 0.65-1.82) compared with those in the delta and delta2 cohorts.

“The major conclusion to our research was that many more children were infected with omicron when compared to delta, but the children who are infected are not impacted as severely as were children infected with the delta variant,” co-author Pamela DavisMD, PhD, the Arline H. and Curtis F. Garvin Research Professor at Case Western Reserve University School of Medicine, said in a press release. “However, because there are so many more children infected, our hospitals were affected over the winter months by an influx of young children.”

Researchers previously reported in MMWR that COVID-19 hospitalizations among children aged 0 to 4 years increased fivefold during the omicron wave compared with the peak of the delta wave.

“Our data suggested that omicron was five to six times as infectious as the delta variant,” Xu said. “When comparing outcomes, it is important to match patients. Our data showed that children infected with omicron were different from those infected with delta. After extensive matching for demographics, socioeconomic determinants of health and comorbidities, children infected with omicron had significantly lower risk for severe outcomes including hospitalizations than similar children infected with the delta variant.”

Reference:

Omicron ‘less severe’ than Delta for children ages 4 and younger, study suggests. https://www.eurekalert.org/news-releases/948532. Published April 1, 2022. Accessed April 7, 2022.

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