Here is Oregon State, Linus Pauling Institute. Immunity In Brief. They begin with Omega 3 to help reduce inflammation. I don’t think they give a dose, I don’t remember. Personally I would follow the label directions which are going to tell you to consult your doctor before taking if you are on medications, (and I would say particularly for a dose of 5 grams. ). https://lpi.oregonstate.edu/mic/health-disease/immunity-in-brief If you are 60 or over, or have some other problem, then I think it would be even more important to consult your doctor first. https://lpi.oregonstate.edu/mic/health-disease/immunity-in-brief
Remember Vitamin E and A can give some “thinning” and so can many herbal products. And obviously one must take into account other OTC products like aspirin and other NSAIDs.
This just addresses Immunity in Brief according to the above article and not whether this will help prevent pneumonia in association with COVID 19, since the FDA is very strict on supplements being touted for COVID19.
Bottom line: consult your doctor first. They know your medical history.
PS to be more specific the OSU article says, “EPA and DHA have an overall anti-inflammatory effect.” see the link.