Infants younger than 6 months of age with COVID-19 were found to have significantly increased SARS-CoV-2 viral loads compared with any other age group, according to results of a study published in The Journal of Infectious Diseases.

Investigators analyzed the viral loads from SARS-CoV-2-positive nasopharyngeal swab samples collected from infants and young children at public and private health institutions in Buenos Aires, Argentina. Samples were considered positive if cycle threshold (Ct) values were less than 36 for both the open reading frame of 1ab (ORF1ab) and nucleocapsid polyprotein genes. In addition, Ct values were used as a proxy for SARS-CoV-2 viral load, and the cohort of positive samples was segmented by 10-year intervals.

A total of 45,318 SARS-CoV-2-positive nasopharyngeal swab samples were identified between October 2020 and June 2021. Among patients (n=528) aged 9 years and younger, the median Ct value of the ORF1ab gene was 27.19 (IQR, 21.5-34.09), which was significantly increased compared with any other age group (P <.001). The investigators performed a subgroup analysis and stratified patients by age into 4 groups: 0 to 6 months, 7 to 12 months, 1 to 4 years, and 5 to 9 years. They subsequently found that the median Ct value of ORF1a among patients (n=46) in the 0 to 6 months age group was significantly decreased compared to any other group, including adults (20.77; IQR, 18.1-26.87).

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This study was limited by its use of Ct values as a proxy for SARS-CoV-2 viral load, meaning the raw Ct values reported here cannot be directly compared with those obtained under different assay conditions.

According to investigators, known confounders of viral load determination such as differences among age groups in the median Ct values for the internal control gene (RPP30), time between symptom onset and sample collection, displacement of circulating variants by the Delta variant, or differences in vaccination status, could not account for these results. Of note, the number of patients with symptomatic SARS-CoV-2 infection was similar among all age groups.

According to the investigators, “[these findings raise] new questions regarding the role of infants in the spreading of SARS-CoV-2 infection.” They concluded that it remains to be seen whether these findings “reflect [an insufficient] ability to control SARS-CoV-2 replication at the upper respiratory tract.”


Ochoa V, Erra Díaz F, Ramirez E, et al. Infants younger than 6 months old infected by SARS-CoV-2 show the highest respiratory viral loads. J Infect Dis. Published online November 24, 2021. doi: 10.1093/infdis/jiab577. 

This article originally appeared on Infectious Disease Advisor