[onewhippedpuppy]

The point wasn’t that being inside has anything to do with immunity to CV. The point is that people who have been holed up inside are far more likely to contract things like the common cold or have allergy issues because their immune system is repressed. Though you certainly won’t build herd immunity to CV by hiding inside. As for the flu vaccine, I’ve read that on a good year the vaccine might cover 50% of the active flu strains, because the flu has many forms and also mutates regularly.