Early antiviral response in nose may determine severity of C
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The course of severe Covid-19 may be determined by the body's antiviral response to initial infection, according to a study which opens up new avenues for early drug interventions that could prevent severe disease. Researchers analysed whether the path towards severe disease could start much earlier than expected, perhaps even within the initial response created when the virus enters the nose.

They studied cells taken from nasal swabs of patients at the time of their initial Covid-19 diagnosis, comparing patients who went on to develop mild Covid-19 to those who progressed into more severe disease and eventually required respiratory support. The findings, showed that patients who went on to develop severe Covid-19 exhibited a much more muted antiviral response in the cells collected from early swabs, compared to patients who had a mild course of disease.

To understand the early response to infection, the team collected nasal swabs from 58 people. Thirty-five swabs came from Covid-19 patients, taken at the time of diagnosis, representing a variety of disease states from mild to severe. Seventeen swabs came from healthy volunteers and six came from patients with respiratory failure due to other causes. The team isolated individual cells from each sample and sequenced them, looking for RNA that would indicate what kind of proteins the cells were making a proxy for understanding what a given cell is doing at the moment of collection.

First, the team found that the antiviral response, driven by a family of proteins called interferons, was much more muted in patients who went on to develop severe Covid-19. Second, patients with severe Covid-19 had higher amounts of highly inflammatory macrophages, immune cells that contribute to high amounts of inflammation, often found in severe or fatal Covid-19.

Since these samples were taken well before Covid-19 had reached its peak state of disease in the patients, both these findings indicate that the course of Covid-19 may be determined by the initial or very early response of the nasal epithelial and immune cells to the virus. The lack of strong initial antiviral response may allow the virus to spread more rapidly, increasing the chances that it can move from the upper to lower airways, while the recruitment of inflammatory immune cells could help drive the dangerous inflammation in severe disease.

The team also identified infected host cells and pathways associated with protection against infection --cells and responses unique to patients that went on to develop a mild disease. These findings may allow researchers to discover new therapeutic strategies for Covid-19 and other respiratory viral infections.

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