Avoiding stress is preventing virus infection
Sheldon Cohen is an expert on the common cold and cold viruses. Among other things, he discovered that happiness, sleep, parenthood [Psychosom Med. 2012 Jul-Aug;74(6):567-73.] and social support [Psychol Sci. 2015;26(2):135-47] weaponize the immune system against the common cold. If there is anyone who knows how we can protect ourselves from the coronavirus, it is Sheldon Cohen. And indeed. As early as 1991, he published a human study in the New England Journal of Medicine that showed how avoiding stress reduces the chances of becoming infected with a coranavirus.Study

This intro was a bit misleading. It was true, but it suggested that Cohen had investigated the coronavirus that is currently decimating the world's population. And that is of course not the case.Cohen investigated the effect of stress on the risk of infection with five common cold viruses - one of which was coronavirus 229E [CV in the figure below]. That's a different coronavirus than the Covid-19 virus.
The other viruses were rhinovirus type-2 [RV type 2], rhinovirus type-9 [RV type 9], rhinovirus type-14 [RV type 14] and the respiratory syncytial virus [RSV].
Sheldon and his colleagues trickled the viruses into the noses of a total of 394 subjects, then watched what happened. Using questionnaires, they determined how much psychological stress the subjects were experiencing at that time in their lives, and on this basis determined the Psychological-Stress Index of the subjects.
The higher the Psychological-Stress Index, the greater the chance that the subjects got a cold.

Above, the researchers have broken down the chances of catching a cold by the type of virus. Psychological stress increased the risk of illness for all virus types.Conclusion
"The consistency of the stress-illness relation among three very different viruses - rhinovirus, coronavirus, and respiratory syncytial virus - was impressive", write the researchers.

"This observation suggests that stress is associated with the suppression of a general resistance process in the host, leaving persons susceptible to multiple infectious agents, or that stress is associated with the suppression of many different immune processes, with similar results."
"The results also suggest that infection and reinfection may be effectively prevented by its daily use throughout the year, with an enormous potential savings to national industry in terms of reduced sick days. This product clearly exhibits excellent antiviral activity and warrants further investigation to determine the nature and method of its viral destruction."
That's clear. If you want to protect yourself from the coronavirus, avoid stress. For some people, it will be easier said than done in these anxious days.
N Engl J Med 1991; 325:606-12.