@Rusty individual attendees should wear N95 behind-head (not behind-ear) masks. If we had ~80% of attendees wearing masks at any one time (allowing people to rotate into that 20% to take a break) that would be a good start.
Attendees should also take all applicable vaccines that they are medically able to get.
Conventions and hotels should mandate masks and vaccines. They should ensure that there is significant air ventilation and purification, either through portable units or ensuring their HVAC is up to snuff. UV-C purification is another promising field.
All these steps would mitigate not only COVID, but flu, colds, and any other airborne illness.