This question has been settled with a final result: "Only after vaccination". Trading has finished.
"I believe that humanity will beat this pandemic, but only when most of the population is vaccinated. Until then, life will not return to normal. [...] Airports won’t have large crowds." [1]
We define 'large crowds' as at least 80% of capacity prior to the pandemic. We also define in favour of Bill that such vaccine must just be available, irrespective of whether people choose to vaccinate.
[1] The Economist - "The world after covid-19. Bill Gates on how to fight future pandemics" by Bill Gates. 23 Apr. 2020
[2] Bureau of Transportation Statistic Releases - "September 2020 U.S. Airline Traffic Data"