Considering that the government has been suppressing ANY and ALL research on MJ, it seems a bit early, if not convenient for those who like the War on Drugs, to have such a concise conclusion that "THC suppresses immunity to COVID-19".
Admittedly, High Times is not an ubiased source but here is a more balanced view on the subject, IMO.
Scientific research is proving more and more medical uses for cannabis. Experts cite medical marijuana as an effective treatment to use in conjunction with other medications, often to decrease their side effects. For example, people with epilepsy, cancer and HIV frequently use cannabis. Furthermore, many people choose to smoke weed instead of drink alcohol when they’re sick. But does cannabis affect your immune system? Here’s what we know so far.
It's a question that isn't brought up often but still warrants investigation. Does cannabis affect your immune system?
hightimes.com
To summarize: Some studies show it helps, some show it does not help immunity.