It proved effective during SARS Cov-1 outbreak. Critical patients were treated using Nitric Oxide which not only improved lungs health but also improved immunity. Now clinical trials are being conducted to treat SARS Cov-2. Hopefully it will be effective in treating novel coronavirus patients. https://www.webmd.com/lung/news/20200409/nitric-oxide-invest...

Remember it is also important to control O2-(superoxides) since NO + O2- = ONO−2 (perixoynitrite)

And that can lead to higher cytokine levels https://www.jbc.org/content/277/3/2330

which are helpful to a certain extent...