Many people infected with COVID-19 have only upper respiratory symptoms, which suggests that local immunity has restricted the viral load to the nasopharynx.
One study investigated the early immune response by taking nasopharyngeal swabs from 58 people who were categorized as mild-moderate disease versus severe disease.
In patients with mild to moderate disease, epithelial tissue expressed antiviral and interferon-responsive genes. Although the viral load is the same, these reactions are attenuated in individuals with severe COVID19.
Despite having the viral load constant in both groups, epithelial tissue expressed antiviral and interferon-responsive genes in patients with the mild-to-moderate disease compared to those individuals with severe COVID19 where these reactions are attenuated.
In conclusion, the study demonstrates that failed nasal epithelial antiviral immunity is the basis for severe COVID19, and the immune reaction in the nasal mucosa is an important determinant of the overall disease trajectory.
Source: https://www.nature.com/articles/s41577-021-00610-2.pdf?origin=ppub
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