In 770 there was first moitzei shabbos selichos, a week later the washing machines for Rosh Hashanah and Yom kippur, followed by dancing every night for a week straight, followed by 3 times hakofos which is approximately 15 hours of sweating together, dancing, drinking from the same cups, sharing the same bites of pickles, sharing the same bottles of water... of course no masks.. With the climax of 2k+ people jammed together for the farbrengen...
that's with 2k+ of people from all over the world, plenty of them not yet exposed. Keep in mind, most people in crown heights got it over 6 months ago...
WhileI 'm not saying that all of this is normal behavior, the fact that this did not bring to hundreds of cases, the minimum this proves is that whoever had the virus once definitely does not need to be paranoid.