Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected more than 180 million people since the onset of the pandemic. Despite similar viral load and infectivity rates between children and adults, children rarely develop severe illness. Differences in the host response to the virus at the primary infection site are among the mechanisms proposed to account for this disparity. Our objective was to investigate the host response to SARS-CoV-2 in the nasal mucosa in children and adults and compare it with the host response to respiratory syncytial virus (RSV) and influenza virus. We analyzed clinical outcomes and gene expression in the nasal mucosa of 36 children with SARS-CoV-2, 24 children with RSV, 9 children with influenza virus, 16 adults with SARS-CoV-2, and 7 healthy pediatric and 13 healthy adult controls. In both children and adults, infection with SARS-CoV-2 led to an IFN response in the nasal mucosa. The magnitude of the IFN response correlated with the abundance of viral reads, not the severity of illness, and was comparable between children and adults infected with SARS-CoV-2 and children with severe RSV infection. Expression of ACE2 and TMPRSS2 did not correlate with age or presence of viral infection. SARS-CoV-2–infected adults had increased expression of genes involved in neutrophil activation and T-cell receptor signaling pathways compared with SARS-CoV-2–infected children, despite similar severity of illness and viral reads. Age-related differences in the immune response to SARS-CoV-2 may place adults at increased risk of developing severe illness.

RationaleDespite similar viral load and infectivity rates between children and adults infected with SARS-CoV-2, children rarely develop severe illness. Differences in the host response to the virus at the primary infection site are among the proposed mechanisms.ObjectivesTo investigate the host response to SARS-CoV-2, respiratory syncytial virus (RSV), and influenza virus (IV) in the nasal mucosa in children and adults.MethodsClinical outcomes and gene expression in the nasal mucosa were analyzed in 36 children hospitalized with SARS-CoV-2 infection, 24 children with RSV infection, 9 children with IV infection, 16 adults with mild to moderate SARS-CoV-2 infection, and 7 healthy pediatric and 13 healthy adult controls.ResultsIn both children and adults, infection with SARS-CoV-2 leads to an interferon response in the nasal mucosa. The magnitude of the interferon response correlated with the abundance of viral reads and was comparable between symptomatic children and adults infected with SARS-CoV-2 and symptomatic children infected with RSV and IV. Cell type deconvolution identified an increased abundance of immune cells in the samples from children and adults with a viral infection. Expression of ACE2 and TMPRSS2 – key entry factors for SARS-CoV-2 – did not correlate with age or presence or absence of viral infection.ConclusionsOur findings support the hypothesis that differences in the immune response to SARS-CoV-2 determine disease severity, independent of viral load and interferon response at the primary infection primary site.

We report on a 10-year old previously healthy boy who exhibited a fulminant and nearly monophasic clinical course of demyelinating encephalitis with relapsing intracranial hypertension syndrome. Histologic examination of a diagnostic brain biopsy revealed an inflammatory demyelinating process with perivascular T lymphocytic infiltration and axonal damage reminiscent of multiple sclerosis-like lesions. In the brain, the DNA of human Herpes virus 6 (HHV6) was detectable. Eleven months after the initial symptoms and on maintainance with oral steroids, MRI showed demyelination of both hemispheres as well as demyelination of the brain stem and Wallerian degeneration. The boy exhibited a severe neurologic defect syndrome. The clinical and radiological course is unusual because of the asymmetric progression of the encephalitis and the extensive confluent lesions without demarcated border or enhancement of the rim after injection of gadolinium. The clinical course showed no definite steroid response. The pathogenetic relevance of HHV6 remains elusive. Although single patients with HHV6-associated encephalomyelitis have been reported, HHV6 DNA is occasionally detected in brains of healthy individuals.

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