They wouldn't dream of canceling the event of course, which is the best way to prevent spread.
However, we could have required and provided #HighQualityMasks, testing prior to the event (with folks submitting results), testing upon arrival, and testing post event with #ContactTracing.
The venue had great ventilation so the addition of a mask requirement and #CovidTesting would have gone a long way in preventing a lot of spread. 
Prior to the event, multiple staff members also got Covid, and it led to a lot of issues with planning and prep, in addition to exposing multiple folks to Covid. This could have also been prevented if our office still required folks to #MaskUp when in the office.