What was “social distancing’ called during the 1918 Spanish Flu epidemic?

According to MW, "social distancing" entered English in 2003, probably during the 2003 outbreak of SARS (that other coronavirus).

As far as I can find, there wasn’t a comparable phrase used in 1918. Plain English was used. Here’s a pretty typical example:

Do not trifle with Spanish influenza symptoms. The situation is positively dangerous here. You are warned to keep away from ALL crowds, in the open air as well as indoors. Do not waste time in restaurants. KEEP CLEAN! Wash your hands before eating. Don't use towels or napkins used by others. Keep the air circulating well in home and office. Do not breathe in other people's faces. Sneeze and cough into your handkerchief. It you catch cold, STAY AT HOME...

_{The Seattle star., October 08, 1918}

When talking about staying at home specifically, there were some specific phrases used, such as isolation and voluntary quarantine (which were mostly recommended for people who had symptoms, even without a diagnosis).

(You may have noticed that circulating air is a recurring theme here. I think the idea is that it would dilute the virus in the air. Apparently, this was such a strongly held belief that open windows were enforced by regulation.)

Many newspapers from this time are freely available, so I suggest you take a look for yourself too. Elephind is a great search engine for this.