The vaccination is important, but it is not magic. It doesn't give 100% immunity, it may only offer partial protection against the known variants, and there's always the risk of a new variant showing up that evades the vaccine. Masks and testing aren't magic, either - they just improve the odds. It is always a numbers game, and the higher the numbers the bigger the risks. Come the summer, the #1 risk is likely to be a new variant emerging and spreading half way round the world (or even half way round a large country like the US) before it is picked up.
If the vaccine means that, come June, people can (e.g.) go to restaurants with small groups and shops can open normally, that will be a major win... but those are modest risks compared to these huge national/international conferences where thousands of people from scores of countries (read: scores of wonderfully diverse petri dishes for breeding new variants) rub shoulders.
Sorry, but huge exhibitions/conferences like this need to go the way of the dodo. They're already partly obsolete when anybody and their dog can launch an Internet "event" which anybody in the world can attend at their leisure.