That isn't necessarily the case. I read an article the other day that was interviews with people who tested positive but never developed antibodies at all. Others who got sick, quarantined, followed all of the CDC guidelines, etc. and still caught it a second time. And I heard just today on NRP where an epidemiologist was being interviewed about potential vaccines and she said that so far it's looking like you may have to get vaccinated multiple times a year until this thing is eradicated completely because the antibodies have a rather short half life and seem to disappear 100 x's faster than, say, the regular flu for example.