Quercetin sabotages influenza virus
In test tubes, quercetin, a flavonoid found in many plant foods, makes it difficult for influenza A viruses to infect cells. Chinese virologists from Southern Medical University report this in Viruses. Is quercetin an antiviral agent?It's working!
The Chinese exposed kidney cells to the influenza viruses A / Puerto Rico / 8/34 (H1N1), A / FM-1/47/1 (H1N1) and A / Aichi / 2/68 (H3N2). The figure below refers to the production of the virus protein hemagglutinin by the kidney cells after they had been exposed to the viruses.

Viruses invade cells, forcing them to make more viruses. More hemagglutinin means more virus reproduction by the affected cells. Quercetin exposure inhibited this process. The higher the concentration of quercetin, the greater the inhibition.

How it works
In another series of experiments, the Chinese determined the infectivity of the viruses under two different conditions.

One condition implied that the researchers first exposed the cells to quercetin and only then brought the influenza virus into contact with the cells. The other condition involved exposing the viruses to quercetin first, and only then exposing the viruses to the cells.
The figure below shows that the latter resulted in the greatest decrease in infectivity. Quercetin therefore directly attacks the virus itself, the researchers conclude.

The researchers think that quercetin turns off the viral protein hemagglutinin. With that protein, influenza A viruses stick to the cells they want to infect. If that protein does not work properly, infection becomes a lot more difficult.Conclusion
"In our study, we found quercetin possessed anti-influenza activity," the researchers summarize their findings. "The study showed quercetin may be developed as a future therapeutic option for the therapy and prophylaxis of influenza-A-virus infection."

Whether quercetin also works in vivo, the study does not say. And if that would be the case, it does not mean that quercetin can inhibit the Covid-19 virus as well. Different type of virus...
More coming soon.
Viruses. 2016;8(1):6.